Kalogeros, meaning "the Monk" is a 60m tall rock stack composed entirely of columnar jointed basalt.  Each column is a polygonal prism, formed by the contraction of volcanic lava during cooling.

Individual columns are about 20 cm in diameter, for the most part, however larger columns in the lower right are 50-80 cm in diameter.

Similar rocks occur at Glaronisia and Sikia.