Osiou Gregoriou monastery, Orthodox monastery on Mount Athos peninsula, Greece

Osiou Gregoriou is built by the sea on a corner of land jutting into the Aegean, on the southeastern side of the Athos peninsula, with steep rocks behind it. The monastery ranks seventeenth in the Athonite hierarchy. Its main church is dedicated to Saint Nicholas, and the complex holds fourteen chapels, seven inside the walls.

Saint Gregory the Young, a student of Saint Gregory of Sinai, founded the monastery in 1310. This establishment made it the seventeenth monastery in Mount Athos' hierarchical order.

The monastery is dedicated to Saint Nicholas the Wonderworker, and Saint Anastasia of Rome is considered its third patron saint because her relics are kept there. The monks support themselves by making traditional Athonite incense and handmade olive oil soap, and the community is known for publishing theological and pastoral books.

The site is built on a rocky coastal slope requiring endurance when navigating stairs and narrow passages between buildings. Sturdy footwear and adequate time are essential for viewing the various chapels and exploring the compound at a comfortable pace.

The monastery keeps the only surviving manuscript of The Shepherd of Hermas, a Greek text written in Rome in the first half of the 2nd century AD. It was found in the late 19th century and published by the Metropolitan of Philadelphia. The library also holds about 300 manuscripts, 11 of them on parchment, and some 20,000 printed books.