Located in the hills above Mandraki, the Monastery of Agia Triada (Holy Trinity) is an example of the simple and austere monastic style of architecture.
Agia Triada is thought to have been founded in 1704 by Antonios Oikonomou, a priest and the grandfather of a naval captain who initiated the Greek Revolution against the Turks on Hydra. Originally a convent for nuns, it was later transformed into an monks’ monastery, which is only accessible to male visitors on one day of the year. During the Revolution of 1821, the monastery contributed financially to the Greek cause, and in 1825, Greek revolutionaries fortified the building against possible attack.
Agia Triada has undergone renovations in 1915, after a severe thunderstorm destroyed the dome and roof of the katholikon, and between 1970 and 1974. The katholikon of the monastery is located in the centre of the yard, surrounded by cells, a world-famous library, a dining room, and other buildings.
Today the complex is uninhabited.