We've seen our fair share of glitches that take you under the game world's map, and Batman: Arkham City is no exception!
Using some clever parkour, Batman can maneuver himself under Arkham City's buildings, looking up from below.
What makes this particular instance of this glitch entertaining is that you can seemingly glide forever!
The creator of the video explains how this is done in the information section, and also points out a practical use in using the infinite space to attain the "dive for 50 meters" achievement/trophy.
Fun and productive!