The Križna Cave (Slovene: Križna jama, literally meaning the Cave of the Cross) is a cave located in the Lož Valley, Slovenia. The cave is particularly noted for its chain of twenty-two subterranean lakes of emerald green water. The cave was first documented in 1832, but the part of the cave which includes lakes and stream passages was first explored by Slovene cavers in 1926. At Kalvarija the cave splits into two branches – the Blata to the north and the Pisani Passage to the north-east. The passage through the Blata is harder so most explorers choose to continue along the Pisani Passage, which requires the use of small boats. The Križna Cave continues into the New Križna Cave.
In the direction from the entrance to the cave, the Pisani Passage is the left gallery of the Križna Cave at the confluence with the Blata at Kalvarija. The access requires the use of boats. Part of the way along the Pisani Passage is a side gallery named the Matjaž Passage (Matjažev rov) and contains several large columns. Continuing along the Pisani Passage the explorer enters the Crystal Mountain (Kristalna gora), the largest room in the cave. The explorer can climb the mountainous pile of collapsed rocks to a point well above the stream.
With 44 species of organisms the Križna Cave is the fourth largest cave ecosystem in the world by biodiversity.
