Monastery of St Demetrios Aygou, Protected Byzantine monastery in Ermionida Municipality, Greece.

The Monastery of St Demetrios Aygou stands near the village of Didyma in Argolida. Its surviving catholicon is a two-aisled church cut into the rock on three sides, except the north and part of the west facade. It has a three-conch bema with a dome, a cross-vaulted nave, and brickwork that remains visible where fire damaged the plaster.

The monastery's origins go back to the 11th century, but its founding year and most of its history are unknown: it appears in few surviving modern documents kept in the General State Archives. Like many others, it was dissolved under the regency of Otto. A 19th-century fire destroyed the carved gilded iconostasis and brought down the vault plaster, ruining the wall paintings.

The cave beside the monastery, used as an ossuary and dedicated to the Transfiguration of the Saviour, holds an 11th-century wall painting of the Virgin with the Christ Child between Saints Anna and Kyriaki. Other frescoes in the same cave are much later, from the 17th century.

Access is on foot from Karnazeika near Iria to the west or from Pelei to the east, near the village of Didyma. The surviving katholikon is cut into the rock on three sides, so the approach passes close to the cliff face. The nearby cave used as an ossuary, dedicated to the Transfiguration, lies beside the monastery.

Beside the catholicon lies a cave that the monastery used as an ossuary, dedicated to the Transfiguration of the Saviour. It is one of the two crater-like dolines for which Didyma is known, and it keeps an 11th-century wall painting of the Virgin and Child flanked by Saints Anna and Kyriaki, with later 17th-century paintings on the same walls.