The only cave of this speleological complex connecting with the outside is the massive La Grave, which is 330 feet long, 170 feet wide, and 200 feet deep. La Grave creates a huge natural pantheon with its opening that lets the sunlight pass through, creating a magical effect where the light moves differently according to the time of the day and the season. The light first illuminates the walls, then the stalagmites, and finally the irregular ground of the cave floor.

La Grave, and the entire cave system, probably originated about a hundred million years ago when the land that now forms Apulia began emerging from the sea. The new land was too rigid and fractures formed, with water infiltrating the soil and slowly creating larger and larger cavities.