Red Lake (Croatia)

Red Lake (Croatian: Crveno jezero) is a sinkhole containing a karst lake near the city of Imotski, Croatia. It is known for its numerous caves and remarkably high cliffs, reaching over 241 metres above normal water level and continuing below the water level. The total explored depth of this sinkhole is approximately 530 metres with a volume of roughly 25-30 million cubic meters, thus it is the third largest sinkhole in the world.^[1] Water drains out of the basin through underground waterways that descend below the level of the lake floor.

• http://en.wikipedia.org/wiki/Red Lake (Croatia)