The "Dark hole" is the name of a cave in Stara Planina, Bulgaria.

It is a system of two main galleries with adjacent parts. Longer is the northeastern part of the cave, about 800 m on the main axis, along the main underground river. Galleries are wide and tall with a predominant rectangular and inverted trapezoidal cross profile. The gallery in the west-northwest direction, with no branches and floors, is about 710 meters long.

Usually, the river drains underground through the cave-shaped Karst spring, Zhiitolyub, but during extreme rainfall and snowfall it raises its level and runs through the entrance to the cave. Built in the series of cracks in the area, the Dark hole cave consists of two main galleries, joined together and very transversal, the entire system being located on four floors, without considering the first yet undeveloped floor under which the underground river flows, leaving Lake Zhekovo.