Katafyki (Greek: Σπήλαιο Καταφύκι) is a cave located in Dryopida on the island of Kythnos in the Cyclades.

It also bears the name "Giorgos Martinos Cave" in honor of the geologist who studied it.

[2] More than 600 meters of the natural cave have been mapped, which, having served as a mine, has a 2000-metre-long man-made gallery.

In several places there are visible remnants of the cave's previous use as a mine, such as rails, wagons, etc.

Iron mining in modern times lasted from 1835 to 1940, while after 1910 exploitation was carried out by foreign companies.