I just want to add:

  • 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.