The Frasassi caves are underground karst caves located in the territory of the municipality of Genga, in the province of Ancona. The set of caves falls within the Regional Natural Park of the Gola della Rossa and Frasassi.
The complex is made up of a huge series of underground rooms of which the first, which can be easily visited by the public, is the Ancona Abyss, a huge cavity that has an extension of 180×120 m and a height of 200 m; it is so large (over two million m³ of volume) that the Duomo of Milan could easily be contained within it.
Inside the karst cavities you can admire natural sculptures, formed by calcareous stratifications over 190 million years thanks to the work of water and rock.
In the caves no natural surface light penetrates at any point, so the lighting is completely artificial.