0 Secrets.

Dear, dear... not off to a very good start!

5 Secrets

Secret 1 : Blow up the first set of dynamite barrels you encounter, grab the Body Armor and Bundle of TNT. There's a hidden switch behind the wooden stand, hit it and a hidden door opens on to the left.
Contains : A zombie hunting down two civilians. Oh, and also there's a Fire Armor and two Life Essences. Not bad for the first secret of the campaign, not bad at all. The well leads you to the only underwater area of the level.

Secret 2 : After you see a bridge spontaneously exploding in front of you, turn right and ahead to the edge of the cliff, there's an opening a tad above you, to the right.
Contains : A cute set of five candles and a Life Seed. Oh wait, is that supposed to be a pentagram?

Secret 3 : When you get up the elevator and onto the top of the huge water pool, the cliff starts to crumble down and make a path up from the water pit. Head down that pit and turn right. That's right, by the looks of that crack the wall can be blown out of your way here.
Contains : There's a Case of TNT lit by an ominous light descending down to the mines from the surface.

Secret 4 : Right after Secret 3, head back up the steps and into the small waterfall.
Contains : Two Bundles of TNT and a Doctor's Bag.

Secret 5 : After getting away from the tight entrapment with the zombies, you get to a storage area. Head to the other end of the storage following the right wall, and you should see a interesting window full of skulls in the wall, try pushing it to raise the wall.
Contains : Body Armor and a doorway back to the room where you got your very first flare pistol.

4 Secrets

Secret 1 : After you get in to the house, go upstairs and check the wardrobe, it has a secret door.
Contains : A double feature of 4 Shotgun Shells and Beast Vision. It looks like they had a helluva party here.

Secret 2 : When in the backyard of the house, go into the lit area in the center. When facing the house, turn left 90 degrees and walk into the forest past the two withered trees. From the right of the second withered tree, there is a fake wall you can walk right through.
Contains : Flare Pistol and a Life Essence.

Secret 3 : Right after you enter the hidden temple, there's an alcove in the wall on both sides of the corridor, check the one on the left.
Contains : Guns akimbo.

Secret 4 : In the corridor leading to the Fire Key -locked door, there's two mausoleums. Check the one on the right, the tomb can be lowered to reveal a secret.
Contains : Sawed-Off and a Life Seed.

3 Secrets

Secret 1 : After getting on the train car carrying the timber (by jumping from the doorway to the Dagger Key-locked car), turn around and check the doorway on the train you just jumped from.
Contains : Limited Invisibility.

Secret 2 : When you leave the passenger car towards the front of the train, go on top of the steamer all the way to the bumper.
Contains : Life Seed.

Secret 3 : In the car with the Innocents in the cage with the Dagger Key, there's a stack of small crates in the corner, the two center ones can be lowered to reveal a secret.
Contains : Doctor's Bag.

7 Secrets

Secret 1 : When entering the Aj Railfreight Co. manager's room, turn right. See above one of the bookshelves is lit up, the others are not. Better check what's behind it.
Contains : Life Seed.

Secret 2 : After entering the museum, head right to the painting of a nun holding a baby in her arms, push it and turn to your right, you should see a part of the wall open.
Contains : Full Drum of Bullets and a Bundle of TNT.

Secret 3 : In the clothing store, jump behind the counter and press on the left cash register. You'll be treated with a gift for being the one-millionth customer!
Contains : Body Armor.

Secret 4 : When entering the air ducts from the clothing store, you find a standable (provided that you stand, of course) alcove after the first jump. It's blocked by a mere grating, blow it away, or just stick it in with your Pitchfork and jump up.
Contains : A Few Bullets and a Doctor's Bag.

Secret 5 : When in the weapon store, flip the switch behind the counter to open a secret door to your left. There's a target board, shoot it to reveal a secret wall on the right.
Contains : Case of TNT.

Secret 6 : In the toy store, flip the switch on the wall near the Fire Key to start a football game. Carefully kick the head into the small basket in the back of the room to reveal a secret on the left.
Contains : 4 Shotgun Shells, Tommy Gun. There's a miniature model of the building right across the street and some children's alphabet blocks spelling "Above you" backwards.

Super Secret : In the toy store secret room, click on the cubes to form the word "ABTOYSAB".
Contains : Life Seed, Super Armour and a way to the secret level.

5 Secrets

Secret 1 : When going up the first elevator, into the room with the Skull Key -locked door. Use the panel near the window to open up a secret.
Contains : Box of Shotgun Shells.

Secret 2 : In the room with the water pump locked with Fire Key and the door locked with Eye Key. There's a round cylinder in the wall near the window, use it to reveal a secret passage.
Contains : Super Armor and a Case of TNT.

Secret 3 : Right after opening the metal gates in the deepest, zombie-infested part of the cellar, there's a waterfall to your right, step in.
Contains : Diving Suit, two occasions of A Few Bullets, two Bundles of TNT and 8 Shotgun Shells in total.

Secret 4 : After getting up from the zombie-infested pits with the elevator, there is a round extension to the wall left from the elevator (the opposing side from the air duct). Use it to reveal a hidden elevator.
Contains : Body Armor, and a Flare Pistol (in a second secret chamber).

Secret 5 : When using the Fire Key to raise the water level, jump right into the water and dive back to the place where you got the key, there's now a small opening opposite from the place where the key stood.
Contains : Life Seed.

6 Secrets

Secret 1 : When you go up the lift with the two railings, just right from the corridor past the candles is a crack in the wall. Blow it up.
Contains : Case of TNT, Box of Shotgun Shells and a Fire Armor.

Secrets 2 & 3 : In the room with the billiard table, the bookshelf on the right can be lowered. Or either access the secret from the second level of the main hall.
Contains : Super Armor.

Secret 4 : In the same secret corridor with the Super Armor, there's a switch to lower an elevator and open a doorway to the lobby, there you can jump on the opposite corners.
Contains : Full Drum of Bullets and a Case of TNT.

Secret 5 : From either corner, jump to the last one with no items on it. You can open the wall here.
Contains : Two Full Drums of Bullets and a Deathmask!

Secret 6 : After entering the room locked with Dagger Key and flipping the switch to reveal the zombies. A chamber right from the switch has a grey back wall, open it.
Contains : Doctor's Bag and a Bundle of TNT.

0 Secrets

How boring!

6 Secrets

Secret 1 : When you dive in the the pool and swim into the smaller corridor, there's a wall that's tinted green on the left hand side.
Contains : Scuba Gear and A Few Bullets.

Secret 2 : The door to the women's bathroom is already open when you enter, close it and it reveals a secret.
Contains : Full Drum of Bullets.

Secret 3 : When you go down the round staircase with the surprising amount of cultists, turn left. There's a scary face painting at the end of the corridor, click to open.
Contains : Guns Akimbo.

Secret 4 : In the men's bathroom, kneel down and shoot the cultist behind the door so that he'll come out to kill you.
Contains : Life Seed and two Spray Cans.

Secret 5 : In the men's bathroom, there's a button on the left side of the centermost urinal. Press it to open a hidden doorway the end side wall near the showers.
Contains : Two Bundles of TNT and a Beast Vision near the ... ermh, window.

Secret 6 : Get on the smaller segment of the dividing blue wall and face away from the manager's office where you obtained the Fire Key, you can see a small blue switch on one of the pillars near the pool, shoot it.
Contains : Super Armour.