Air Rooms which drop you to the room below if you are in them, giving you a Falling flag, which accumulates a counter based on how far you traveled. Until you are in an object that has no Air room flag, then it generates damage based on how many rooms you fell, with a constitution roll to attempt to reduce it.
Rooms can also have the CLIFF flag which makes them climbable. By default, you are unable to travel to a cliff room or an air room. However, you can use the climb command to carefully move to cliff room, giving you the CLIMBING flag (which makes you not fall in cliff rooms). However, this won’t work in urban settings, so really think it carefully on how to do it.