Secret fishing holes
When you first start a new game, go to the first hole on your left and go to the end of it. There will be a small hole where you will be able to see into. Go forward in the game and get a rocket launcher or mines and return. You will be able to get in the hole, swim, and shoot the fish down inside. Go out over the pit where there is a group of guards and the tank that will shoot at you if you do not blow up the bridge. Go down the tunnel and it will lead to a open area, where after you kill all the guards, an elevator will come down. Immediately above the elevator is hole that is difficult to see. Go left of the elevator, go up the hill, and go into the hole. It will lead you around until you get to a large open room with a lot of water with fish, bats flying around the roof, plants on the wall, and a dead miner at the bottom (where there will also be Extra Life and Extra Body Armor).