On the level where you have to find a bunch of key cards in a town with a church, hammonds house, a bunch of a half way built houses, and two buses, there is a way to get access to a secret level. to do this, go to the bottom of the steps in front of the visitors center. at the bottom, turn right 90 degrees. you should see a barricaded gate about 75 yards away a little to your left. go towards it. when you reach it, walk into it, jumping, until you get on top of it. a very good idea would be to save before you attempt this because you can get stuck on the other side of the gate. it happened to me. when you are on top, look right, and go along that wall towards hammonds house and the church. there will be a few niches. go to the second one (or first, one of the two) and walk back and forth over it a few times. if done right, I cant give you any better of a description because it happened to me by accident, if done it more than once though, a new level will load. on this level, there will be about all the guns, an infinite amount of raptors (shoot sign that says raptors to spawn a new one), gold bars, and places that make you say something.