The large entrance hall of this cave conceals a deep, dark mouth, filled by an underground stream that is always well-fed, even in dry periods. This is the entrance—reserved for cave divers—to a vast and intricate network of cavities deep within the mountain. The water is actually clear, and it is thought that the name derives from the dark moss-covered floor, over which the stream flows before flowing into the Senaiga.
Due to the cave's complex morphology and technical difficulties, exploration began only in the 1970s, and so far, cave divers have discovered a 1,600-meter stretch of siphons and difficult passages. In the 1930s, dye injections proved that this cave communicates with the Castello Tesino Caves, a few kilometers away. Furthermore, an examination of the fine sand found inside, rich in granite crystals, testifies to a significant contribution of water coming from the Cima d'Asta group, much higher and much more distant!