Got out of Hidden the standard way (Jumping on the car to the other car to the crate to the 3rd car then over the hedge) Also, if you get out of Hidden, jump into what I call the "Pool of no Return" because you can't get back out, you prone and crawl under the textures towards a big building. You can eventually stand up & run. Anyway, when you reach it you'll be sticking out of the ground & moving all over the place, get your friend to down and revive you, then stand up & do the same to your friend. You will now be above ground and you can get into... AN EMPTY ROOM!?!