E1M1: Cradle to Grave

After climbing out of the grave, there is another grave just at your right. Crouch down and push coffin's side to make it slide down.
Contains: A box of flares

There's metallic wall directly front of you, after you hop up from your only temporary resting place. Push it to reveal a secret.
Contains: A box of TNT

After stepping outside of the doors to encounter zombie(s), turn back towards the doors. At left one part of bushes has different colored leaves. Touch it and it slides down revealing a secret place and the empty grave of Eric Draven. You could touch also tombstone and Caleb says: 'Nevermore'.
Contains: A body shield

At to the graveyard front of the chapel there's a tomb with In loving memory written on the side of it. Try to get to the top of the tomb by jumping on the top of nearest tombstone and jumping again to the roof. Somewhat easier way is go inside the chapel, break upstairs window and use graveyard fences as a catwalk.
Contains: Guns Akimbo

When you get to the main hall with altar, walk towards altar over benches. Altar begins to slide towards you and rats burst out from the gap behind altar.
Contains: A box of flares

Behind the curtains near altar room is an organ. Playing with it causes few horrible tunes and a small panel slides up at the front of you over organ.
Contains: Beast vision

From the organ, walk up the stairs towards the next corner. Opposite the window with two bundles of dynamite under it are wall coffins. One of them has a crack in it. Use TNT to blow it open.
Contains: A body shield

At the other end of hallway near two TNT barrels is another crack in wall-coffin at the head level. A nice explosion will open it. A few rats wait you inside the coffin.
Contains: A fire armor

In the crematorium, after you have the fire armor, crouch on the conveyor belt and crawl into the fire. Be sure to get back out quickly!
Contains: Life seed

Near the door leading to the crematorium, there's few equipments for separating body parts in their way to the crematorium oven. Push the saw and shelf at right will slide aside.
Contains: A box of flares

Near the end of the level where zombie climbs out of a stone coffin, behind the coffin's lid leaning to the wall is a secret. Contains: A box of flares
Also don't miss the doctor's bag hidden behind the flesh barrels near the crematorium window, although it's not counted as a secret.

SUPER SECRET: At the very end of the level with two coffins is invisible wall opposite the hole leading inside the chapel. If you don't know what I mean, try to throw dynamites against wall over your head level. At some point dynamite 'goes through wall'. You perhaps could jump there from the edge of the hole leading inside, but at least for me only way in single player to get there is drop a burning dynamite (with Alt-Fire) at your feet when you stand on coffin and jump repeatedly on dynamite. The blast may or may not throw you inside the secret.
Contains: A napalm launcher

In co-operative mode, use your friend's head to get inside! Jump on your friend's head (this may require some practice with crouching and jumping together to make you both enough skilled) and then jump inside the secret. If your friend crouchs and then lifts you up, it makes job easier to you. Try. This is a way to get in nearly any impossible place without boots of jumping.

In single player you can also use monks and monsters as a platform, but it's become pretty dangerous since Blood patch v1.11, monks began to hurl so much dynamite that you're in danger to separate your flesh from your good old spinal cord. Try anyway if you dare.

E1M2: Wrong Side of the Tracks

In the train station waiting hall, pushing the 4th phone from the left will slide it down revealing a secret. Also when phone slides back, it lifts you to the flares, if you won't get them by jumping from benches.
Contains: A body shield

Find your way to the kitchen and blow up the fire extinguisher. Blow up also a lousy zombie rushing out from the wall hole.
Contains: A box of flares

Also in the kitchen, open the cupboard/fridge, remove zombie(s) and push the button with the handprints on it to open another secret area in the room that blowing up the fire extinguisher opened.
Contains: The cloak of invisibility

Go up the left-hand staircase starting from the waiting hall, you'll end up to the dark hallway with friendly pictures hanging on wall. There are windows at the left. Smash one of them and jump out to the secret ledge.
Contains: Life seed

Continue to the end of the hallway in to the room. Behind the picture on the wall is a secret. Beware zombies trying to get you.
Contains: Guns Akimbo

Find your way to the bookstore. By putting your greedy hands on a cash register it will lower two shelves. First one lowers at your sight.
Contains: Doctor's Bag

Another secret is to the right from the cash register at the corner of the room. Press again cash register if shelf closes before you.
Contains: A body armour

On the train platform, go into the No admittance room and blow up it's inhabitants and a crack in the wall. In the hole are another crack, offering some TNT in it makes way to the bookstore. Don't miss two TNT bundles hidden behind the room's opened door, closing the door reveals them.
Contains: A box of shells, a box of flares

In the bar (before the kitchen) rests jukebox. Break your multiplayer buddies nerves by playing some painful tunes.

Want to know what happens when you slip accidentally under train? No worries, man! When you find your train, Phantom 666, and Tchernobog sign, follow the tracks opening at front of you by foot and find out!

E1M3: Phantom Express

In the carriage full of crates, walk straight ahead through the door to the end and jump onto the box, turn around and at your right there is another crate at the ceiling level.
Contains: Life seed

Also in the same carriage, there's a blue chest on the pile of boxes. Put lights on, so you clearly spot it.
Contains: Beast Vision

When entering in the restaurant carriage (last one in the train), the left side bar has a switch near the foot level, which opens a secret panel at the right side bar's wall. Right side's switch opens and closes the curtains.
Contains: Reflective shots

Find your way to the kitchen. Although there's a lot of stuff nearly hidden nearby, the only secret is in the upper oven near the door. You'll need to go inside oven, even you'll get flare gun by opening the oven's door.
Contains: A flare gun

The first room in the passenger carriage has a crack in the corner, blow it up and jump up into the hole. Beware inhabitants there, usually they make more damage to you than it's worth of visiting this secret.
Contains: A tommy gun, several TNT bundles, few boxes of flares

In the locomotive, blow the grate blocking the way inside the engine and jump inside. Run through first another side of oven and then turn back and collect the rest of the stuff in another side. You can open grates in both sides of the engine, if it easies the task.
Contains: A tommy gun, a shotgun, a flare gun, life seed
Contains in multiplayer additionally: A full armour, Guns Akimbo, so try to visit often here

SUPER SECRET: In the passenger carriage, the second room has now a hole to the outside after you break the wall with TNT. Go to the edge of hole so you'll hang partly outside and look towards the back of the train. Don't drop now, it's instant death, even if you have a full armor and life seed. See the text, Phantom 666? Jump towards it. You should land to the nearly invisible ledge. It's unbeliavably easy to get there, you just don't see that ledge. Push the carriage's wall and it will open. You'll get directly back to the hallway from the secret, no need to jump back.
Contains: A shitload of things: a shotgun, a tommy gun, a full armour, life seed, Guns Akimbo, a really good secret place for multiplayer

Worth of trying: Jump repeatedly when you accidentally leave train without your co-operative willing and hit ground rolling outside train. You lose about one-third of full health with each jump, but you might survive. Try this also with super secret. With life seed and full armour you'll can jump long distances. For being already dead guy for multiplayer adversaries.

E1M4: Dark Carnival

You'll start from a little damaged locomotive. There's another part of it nearby. Three huge fires burns covering a hole in one corner of it. You can go through flames without burning yourself and find some stuff from ex-passenger carriage. You can get there also at another side of level (where are storage boxes and napalm launcher) by blowing hole in passenger carriage just above bench.
Contains: Some TNT bundles, a body armor, a box of shells

Jump to the water when you reach a bridge. Swim to the right under the building and raise to the surface. Beware swimming monks with tommy gun, they sometimes make visiting this secret being unwise decision.
Contains: A flare gun, a shotgun, a tommy gun, Guns Akimbo

There's a shooting gallery with ducks and smileys. Shoot several targets to get a price. If your aim's not so good, who said that you must use a gun?
Contains: Life seed

At the top of the wagon with text: Rotten Candy is Boots of Jumping. Go to take them and turn to the right. See the fence which is too high to jump over without boots? Without boots: if you haven't yet burned all your bullets with tommy gun to moving & living targets, there may be mime still alive near fence. Use him as a platform.
Contains: Beast Vision

At next there's a mouth and three heads. Well, this is pretty hard secret and you could spoil it by squishing one head, but at first try slowly kick them nearer and then shot them in. If you destroy a head, I don't know if another head's are valid for getting price. Try out.
Contains: Invincibility

At another shooting gallery, shoot the monk and bottles and be awarded.
Contains: Invisibility cloak

At the left of the bottle shooting gallery is a another nearly unreachable fence. Use your Boots of Jumping or jump from upstairs window. However, the jump from window shelf is pretty hard, so go with boots instead.
Contains: A drum of bullets

In the freakshow, blow up the 3rd set of bars (where the ugliest zombie hangs) and use some pitchfork to zombie. A secret panel opens behind you. Try out to torture hanging poor creature with double tommy guns. :-)
Contains: Guns Akimbo

Behind the snake container under Jo-Jo's rope there is a secret door which opens when you push the left side Warning-sign. If you enter, you perhaps recognize familiar character hanging there in a bit poor condition. Trying to push him gives 'Shake it, baby'. After you tick him enough with pitchfork, remember to leave a hissing dynamite. DN3D sucks and badly (just my honest opinion).
Contains: Two boxes of flares, a box of shotgun shells

Inside the ticket selling booth, there's a stack of boxes against the wall. Touch them at the middle to uncover a secret.
Contains: A box of flares, doctor's bag

Near 'Test your strength' Punch-O-Meter is a storage room full of monks and zombies. After you get rid of them, examine carefully the room. You should notice one pile of boxes with scratches on them. Pushing them causes boxes to lower (you must to touch scratch marks, pushing only the box pile won't open it) and you may enter to secret room. Mimes (unfortunately to them) block the way, but that's not a problem.
Contains: Life seed

At the destroyed bridge where you must jump to the water to get to the Tchernobog sign, look at the other side. In the wall is a crack. Use napalm launcher or accurately throwed TNT to blow it up. Then jump from to the pillar to the another until you get inside the hole. If it seems to be hard, jump to the second last pillar and use Boots of Jumping. After a little swimming, you pulp to the surface and notice to be inside a cave containing a stone pole with 3 buttons. By lowering the stone pole game throws you to the secret level, E1M8: The House of Horrors. Remember tapestries around the carneval area? The combination is Knife, Eye, Moon
Contains: Life seed, a full armour

Dump the big trash can near the ticket booth and you'll find Reflective shots. With this you can easily take care zombies and monks charging from storage.

E1M5: Hallowed Grounds

Inside the entrance just past the gargoyle there's a large open hallway with tall pillars at the sides. As you enter this room up on the wall to your left are two designs. Blowing up the left design reveals a hidden area with a doctor's bag in it. This area can only be reached by using the boots and jumping up. If you've used them up then there are some more boots available later in the level.
Contains: Doctor's bag

In passageway with higher platforms on each side is an eye tapestry above door. Aim carefully and shoot directly into eye. You hear when a niche opens behind the door at the right side wall.
Contains: Guns Akimbo

In the same hall where the eye tapestry is located are near roof level (look up) gargoyle statues. Use boots to jump up to the right (...or left?) side one. Gargoyle will animate when you arrive to the ledge, but it's piece of cake if you grab power-up quickly.
Contains: Invulnerability

Again, in the hall is a passageway leading to the outside area. Between outside area and hall are three windows with colored glass, if you don't know what place I'm meaning. There's a ledge around the area. Jump on the ledge and follow it. You come to the small room, where gargoyle waits you.
Contains: A box of flares

Taking a left turn at the bottom of the stairs behind the moon-key door brings you to an elevator. After stepping on, there is an alcove at the right of the elevator with some armor in it.
Contains: A body armor

When you take care of monks guarding the main hall and follow passageway with flames blazing in wall niches at both sides, you arrive at room with doors left and right. At the floor is skull mark. Step little closer the key and wall behind you closes the escape and zombies burst out. Blow zombies to the hell and take Boots of Jumping where they came from. Jump directly up in zombie locker and you'll find a area above.
Contains: Reflective shots

In the area underwater with the switch, wait for a while after flicking the switch and a small tunnel opens up on the wall to the right of the switch.
Contains: Life seed

In the room containing the moon key, there's two pictures on the wall. Push the right one, if looked from the courtyard side. The center columns will raise revealing secret and two gargoyles.
Contains: Full armour

In the courtyard there's a rising stairs leading inside. Follow them and open the door. You see the different wall section, the square tiling? Just rush to the secret.
Contains: Cloak of invisiblity

SUPER SECRET: It's damn hard to get alive into the super secret, so save your game, if you're playing in single player. Walk from the temple to the bridge at the end of the level and turn to the left. Look down. If you won't see a thing, look again at the cliff where the gate and Tchernobog sign resides. At halfway down is a ledge. Don't rush to jump on it. You'll take an incredible amount of damage by only touching the ledge. Instead you should face the wall at the middle of the bridge (at the spot where ledge ends), jump against the wall and whack the open-button. If you at first time manage to open a wall and slip inside, you're good. It takes several times to load the game, until you figure the door's spot. Remember that you must immedialitely get inside the secret or you're dead. Probably you take pretty much damage anyway, so be sure to have nearly 100 health and some body armor on you. When you get through, you will get teleported back on the bridge, so don't try to jump back.
Addition: The closer investigation shows that you take only damage when you touch the ledge. Jumping repeatedly and trying to open the door may be a good approaching tactic. Or to save invincibility powerup.
Contains: Life seed, a full armour

E1M6: The Great Temple

At the start, the zombies will kill themselves by trying to get you. Go to the hole where zombies came from. Turn around. See the black wall at front of you? Actually it's a hole. Go in hole and turn at the left.
Contains: Several TNT bundles

Near the start is the bridge. Later when you raise it, you can jump to it and go to the left. Near the switch is a dark wall, which is clearly different from others.
Contains: Doctor's bag

At the start before you raise bridge up, you must jump to the water. Swim forward and you come under the stone platform with support pillars. There's a lot of spine-fish here. Swim near bottom following the right side. You'll find a small hole there.
Contains: Cloak of invisiblity

Past the area where a stone-face spits a fireball at you after picking up Guns-Akimbo from lowered platform, there is a small area with lots of stone designs on the walls. On one side of the central section is a reddish design, open it to reveal secret.
Contains: A box of shells

In the area where you find the fire key, there is a circular area opposite with a pole in the center. Go around the other side of this pole, look up at it and shoot the button. Area rotates around. You can go out of here by shooting/pitchforking button again or blowing up wall with mark on it.
Contains: A napalm cannon, some TNT, a box of flares, life seed

In the end, where you must execute lot of monsters and monks in the circular area before you can go to the Tchernobog sign, you surely notice the C-shaped moving wall, which lets you visit in each room at a time when you flick the switch. Well, turn the switch and try to run along the wall, when wall hole passes teleporter, jump in.
Contains: Invincibility power-up
Contains in multiplayer additionally: Life seed, full armour

SUPER SECRET:At the top of the Temple opens the view above the clouds from the room with two pillars and niches full of zombies. Throw zombies way down, so they won't interrupt you. Save your game, if your playing methods do not consist very accurate moving, there's a long way down. Then, go approximately at to the middle of the opening down and look down. See cloud texture higher than others just below you? Walk very carefully and slowly off the edge and you'll drop on the cloud ledge. Try dropping down near left side of the opening, if it seems to be impossible to get on the ledge. Then, just follow it and you find a door. 'I can't believe you found this, here, have everything' will be displayed and then it's just like shopping with credit card. Teleporter will appear later and it whisk you back to the up.
Contains: Everything! (in SHAREWARE Blood, just remember)

In addition: You can measure the chasm where you throwed zombies. Take Invincibility power-up and jump down. You just never get up again without saved game. There's a text below there if you wish to take a look.

E1M7: Altar of Stone

These are not reported as secrets. They just easier your task.

Walk upwards the stairs to the left side and throw yourself out of the window. You'll drop to the ledge. Teleporter will put you safely back to the starting point.
Contains: Full armour

Repeat the nearly suicidal procedure at the right side.
Contains: Life seed

Before you go up to meet your final challenge, take a walk around the altar pillar. Below the bridge resides the Boots of Jumping. Now, it's time to lure the great gargoyle(s) out. Try to get some distance to them and jump with Boots to the wall hole where they come from. Turn quickly to the right, grab stuff and return to the fray.
Contains: Guns Akimbo, shotgun, a box of shells

E1M8: House of Horrors
When you pass the exit gate, walk straight ahead. Trees before you are just fake and you can go through. Contains: Tommy gun and a drum of bullets Go inside the mouth. You'll end up to the ticket booth. Near the ticket booth is a large sign. Push it and a small closet opens at the right corner. Contains: Full armour At the graveyard with a pool in the corner, there is one tombstone darker than the rest, push it to open a secret niche. Contains: Life seed Near the graveyard there's a door. Go up the stairs and you'll end up to the room with some wood and boxes around. When you enter the room, at the front of you are some wood lying on the floor. Crouch and push them to move them aside. Contains: Guns Akimbo Continue your bloody way and jump out of the storeroom to the outside. Blow the X-shaped planks, blow the TNT barrels and blow the monks. Then, take a look around. There's a ledge running around the area. Jump to the ledge and follow it to the far end. Jump towards the grey wall and you'll find the secret. Contains: Doctor's bag, some TNT Don't miss the doctor's bag in the ticket booth. When you open booth's door, you hide bag from yourself.