The caves of Frasassi are underground karst caves located within the Regional Natural Park of Gola della Rossa and Frasassi in the municipality of Genga, Province of Ancona.
The complex is formed by a series of caves of which the first, that can be visited from the current entrance, is the Ancona Abyss: has an extension of 180 x 120 m and a height of 200 m; is so large (more than 2 million m3) that it could contain the Milano Cathedral with no trouble.
Within the karst caves you can see the natural sculptures formed by layers of limestone over 190 million years through the work of water and rock. Water conveying carbon dioxide in the limestone creates a chemical process that gives rise to calcium hydrogen carbonate.
This phenomenon determines the transfer of small amounts of calcium carbonate from place to place and, in the course of a trickle that lasts millennia, forms concretions of considerable size and shapes sometimes also curious. These are divided into stalagmites (columns that grow progressing from bottom to top) and stalactites (hanging from the ceiling of the cavity).