Caves

Perhaps the most common topographical feature of the Underdark, a cave system consists of a series of caverns and passages that may stretch for miles. Caves can be formed by several different methods, but the most common is the action of flowing water. Cave systems often twist, turn, climb, and drop in a enraging fashion, forming three-dimensional mazes that dishearten even the most determined mapmakers. Caves vary widely in terms of their habitability. Living caves that include streams or rivers are full of life by Underdark standards and can often support surprisingly large populations, especially of improbably large and ferocious monsters. Other caves may be barren wastelands, without food or water.