Tunnels

A tunnel is simply a passage that connects one place with another. Most are cut by creatures, though some are the results of natural movements of the earth and other forces. Underdark races often cut very ambitious tunnels to link multiple cave systems. Though such monotonous passageways may be dozens of miles in length, most are only 10 or 20 feet across. Other tunnels are the work of burrowing monsters such as delvers, purple worms, and umber hulks. These “natural” tunnels may be twisting, turning mazes of intersecting passages.

Tunnels are some of the Underdark’s most useful roads, but they severely restrict a traveler’s options. If you don’t like where a tunnel leads, you really have no choice but to go back the way you came. Tunnels also offer few hiding places for those who cannot blend in with stone, so often the only way to get away from a predator is to run-and hope you’re faster.