Hulen — "the cave" in Norwegian — is exactly that: a student-run music venue and bar inside a Second World War bomb shelter carved into the rock. It has been open since 1968 and is the oldest rock club in Scandinavia. The interior is genuinely subterranean, with low ceilings and rough stone walls, and the acoustics are accordingly interesting.
The programming covers rock, punk, metal, and alternative acts — some Norwegian, some international. Drinks are cheap by Bergen standards because it is a student operation. Not the place for a quiet conversation, but for live music in an unusual setting it is hard to beat. Check their website for the programme.