Not sure if this is can be reproduced, but I thought I'd post it. There was a glitch in the treasure vault map that let me walk outside of the normal boundaries of the terrain. I was scared to explore too far, since I didn't want to get stuck somewhere and have to go back to Emberlight. This happened on Depth 22 of the Silver Phantom gate.
http://wiki.spiralknights.com/images/2/22/GlitchyTerrain.JPG
edit: This happened again on depth 24, same spot.
There doesn't seem to be any harm in exploring, except maybe the inability to find your way back. I ran off to the right for three minutes, trying to test if there was an invisible wall, and it seems that the nothingness goes on forever. Here's what the map looked like before I decided to stop wasting my time and head back:
http://wiki.spiralknights.com/File:OutOfBounds.png