A natural travertine cave of the diameter of 22 meters and the height of 6 meters is located  26 meters under the smallest courtyard.. Existence of the cave is a result of rainfalls that flow in the crater and external crashes into the middle of the travertine hill.

The water disrupted the travertine and washed it away. It formed the present round room of the cave with decoration on its walls. There are two small lakes in the cave that are probably connected with others.

The inhabitants must have known about the existence of the cave because it was used as a shelter and as a water reservoir. It was repeatedly discovered in1888 when the well was cleaned and repaired during the last reconstraction of the castle. The cave was first opened to public in 1967.