Like in the Forest Temple where the staircases are straight and winded, except you don't hit a switch for it to be winded.
Surprises, like when the Yeta turned into Blizzeta. That face was a hella scary.
Hallways that suddenly fade off into darkness, with enemies all around. Map screen goes blank, then you appear somewhere else that you've already been in the temple, like a mini-boss battle.
You get halfway through the temple, then face the boss. You automatically, always, lose. You are taken to a part of the dungeon where you haven't been before, and you have to face the miniboss, with no items or tunic.

The dungeon could be like one big nightmare.