The early christian cemetery of Agios Onoufrios, the only one of its kind in the Peloponnese, lies on the slope of Agios Nikolaos hill. It is carved entirely in the poros bedrock and consists of six burial chambers that comprise both arcosolia, dug into the chamber side walls, as well as pit graves, opened in the chamber floor. Small niches, opened at the root of the arches, were used to place oil lamps in. Benches and offering tables around the side walls are connected with mortuary worship rituals.

The chambers have flat roofs and the arcosolia are shaped as tall blind arches. The walls were originally decorated with wall paintings, very few of them being visible today. During the late byzantine period (12th – 14th century) the cemetery was used as a hermitage. A blocking wall was built in front of the first chamber, which was re-decorated with wall paintings, very few fragments of which are preserved. The cemetery is very similar to the early christian catacombs in Melos, as well as with those in southern Italy and Sicily.