Murder mystery quest - there was quest in district which lead you to the murder. Murder mystery could be imagined in very interesting way involving solving puzzles, getting trapped in a plane and escape it, finding the clues for someone framed, and solving big conspiracy behind it.
Finding strange items which are cursed trap doors to another realm. Player would need to find his way back.
Puzzle boss design - in boss arena there are couple sources of power which render boss immortal. Player needs to find a way to deactivate or destroy those sources in order to fight the boss.