1 facility, obvs.
2 lethal lava land, mario 64
3 spirit temple, ocarina of time
4 the big icy but in metroid prime
5 big boo's haunt, mario 64

multiplayer
1 skyrail, 007 nightfire
2 facility, obvs.
3 yoshi valley, mario kart 64
4. the big zelda one on super smash bros melee
5. horror land, mario party 2

"level" being subjective here, nerds.

SUB-THREAD: has there ever been a decent underwater level in anything ever?