Bullenkuhle, Sinkhole lake in Sprakensehl, Germany

Bullenkuhle is a natural sinkhole within a pine forest near Sprakensehl, spanning roughly 130 meters across and dropping about 15 meters deep. The basin is bordered by steep slopes, while a marsh area occupies the bottom.

The Bullenkuhle is a sinkhole formed by the collapse of rock salt from Permian Zechstein deposits, which leached away in contact with groundwater. Its exact age is unknown; dating would require a stratigraphic and pollen analysis of the vertical profile. Sinkholes like this are geologically young, often only a few thousand years old.

Local legend explains the hollow with a hunter's curse: a farmer who neglected his farm to chase a stag swore his house and yard would sink if he returned empty-handed, and that evening the ground swallowed them. The moor is now a protected area, and up to eight amphibian species and adders live in it.

The hollow lies about 1 km west of Bokel at the edge of a pine forest, with slopes of 30 to 60 degrees. The floating mat covers most of the marsh, leaving only a small open bog pond in the northeast; stay on solid ground and keep off the mat.

The open water left in the northeast is a bog pond, a Moorkolk, only about 400 square metres in size and several metres deep. The floating mat of moss and sedge has closed over almost the rest of the hollow, leaving this small pool as the last stretch of open water.