Marijino brezno is composed of several caverns that reach up to 275 m below the ground and opens south of the Škofja Loka castle. The cave is a labyrinth of sometimes very narrow tunnels. The only larger area is the 130 m long, up to 30 m wide and 13 m high Great Collapse Hall which flows into a narrow and low water tunnel, where water from the cave gathers. The tunnel ends with a siphon, but the stream flows underground into the nearby Sora. The cave mostly developed from Oligocene clays and conglomerates and is the longest cave in such rudiments in Slovenia. Entrance to the cave is closed but is possible if arranged in advance with cavers.