This is a list of the secrets on the map Antediluvian by metlslime (ant.bsp from ant.zip)

Look behind the teleporter right at the starting point of the map.

Reward: 50 Nails

Before entering the first wind tunnel, check the ceiling behind it. There is a shootable button. It removes bars in the previous room letting you access a secret.

Reward: Quad Damage

Right after that wind tunnel (the one that lets you bounce) there is a grating on the wall of the corridor to the right. Jump against it and a part of the floor will open.

Reward: Red Armor

In the pool of water where you landed after taking the silver key (and jumping into the wind tunnel) shoot the grating at the end of the left tunnel-like stub. Then turn around and swim into the right one, part of the floor will retract.

Reward: Rocket Launcher

After the big outside area you pressed a button to extend a bridge below. Jump onto it and you see a Death Knight on a platform. Kill it but stay inside the opening of the wall. Turn around and you will see a shootable button just below the bridge you previously extended. Shoot it and the platform on which the Death Knight stood will lower. Jump on it.

Reward: Megahealth