Kill all trash mobs, leave no one alive, drops something else than 'Tiny Key'

Use said item to unlock special rooms where you are locked until you kill all mobs inside - or discover a treasure, but trapped with puzzle like Temple of Qarn to solve. (broken parchment that needs to be placed in order and read to open it)

- dark room, you must lit all candles in a pentagram fashion, but wind sprites are having fun messing with you, you need to 'comfort' them.. (if pentagram is lit in reversed order.. o.O )

- plates that needs to be move into proper position, else you open the barrier and need to fight the beast..

Using specific skills as well..

- Bard's Song that needs to be done in order, or Monk that uses Mantra (channeling) to siphon all water in the room and gain access to another floor..

Lots of possibilities in here.