At the starting point, jump in and go for a swim. When you can see the gold door, this button is over your head. Shoot. A lift will get you up to the secret.

When you are past the mincer, and out of the well, go right to reach this area. In the ceiling of the sniper platform is a target switch. Shoot it, and ride the lift up to collect your secret.

Finished with #2, get out of the other door, and jump over the side of the bridge. Collect secret. Get up the slope next to the building, a door will open to let you in. You will get a very warm welcome.

From the platform overlooking the start area, jump on the railing, then down on the ledge. Quite a useful little secret

Just too bad you have to get past that damn mincer to get in again...

I hope your jumping skills are up to scratch. Else you can polish them a bit here. When you hit the switch, a box with a goodie opens right next to you.

After honing your jumping skills - and perhaps your first-aid skills as well - this door is open. Jump off the bridge (you have to anyway), and go under it. Useful secret here. Never mind you're wet, have a broken leg and a finely grated bottom...

When you finally reach the ledges over the gold door, one wall texture is 'hanging' a bit. Shoot, and get a goodie.