The Church of Dormition (Kimisi Theotokou), also known as Monastery, stands the middle of the quayside in Hydra's port. It was founded around 1645 as a monastery, based on the plans of Venetian and Genoese architects. It was destroyed by an earthquake in 1750 and it was recostructed a few years later.

Nowdays only the main church functions. It is a basilica with colonnades, impressive decoration and a magnificent three-storey bell-tower made from Tinos' island marble. The monk cells and the rest of the old monastery, house Hydra's Town Hall and a small Ecclesiastic Museum.

In the courtyard there are the statues of Lazaros Kountouriotis, Andreas Miaoulis, King George 1st and Antonis Lignos, created by Dimitri Filipoti. Visitors may also see the tomb of Lazaros Kountouriotis and a memorial from the balcan wars.

ECCLESIASTIC MUSEUM OF HYDRA: The Ecclesiastic Museum of Hydra is housed in the Dormition Cathedral, at the place where prison used to be. It exhibits documents of historic value, jewlery, relics, oblations and icons dating from the18th century. One of the most beautiful exhibits is the icon of Virgin Mary, dating from 1774.