It lies on 1.5 km length. It it the most beautiful system of caves probably in the world. It consists in 4 caves each having a name, each being more beautiful than the other. The most beautiful is at the end "the white cave". There is a long passage (500 m) resembling "the Siq" in Petra, Jordan.
The ticket is 15€ for the long tour 2 hours- which I very much recommend and 10 € the short tour 1 hour. The tours are guided in english, french, italian.
The stalagmites and stalactites are incredible!
It is a must see if you are in Apulia.