I watched this movie a loooong time ago, so excuse me if I'm not very exact.
It was about 4-6 people being in this underground thing. The entrance to this underground house, living place, whatever (I have no idea what to call it) was this cap in the ground. I don't remember much of it, but I remember that they at some point did drugs and drank alcohol down there, but that was later in the movie.
It wasn't a horror movie, as far as I recall.
I know it isn't much, but does anyone have a clue about which movie this might be?