A grand sea-captain's mansion from the late 18th century, halfway up the slope on the west side of the harbour, now operated as a branch of the National Historical Museum. Lazaros Kountouriotis was one of the wealthiest merchants on Hydra and one of the principal financiers of the Greek War of Independence — he spent his fortune outfitting ships and supplying the revolutionary fleet.
The house has been restored to roughly its early 19th-century state: dark timber ceilings, traditional Hydriot textiles, period furniture, and a small gallery of paintings by the brothers Periklis and Konstantinos Byzantios in the upper rooms. The walled garden behind the house is one of the few green spaces in the centre of town. A useful counterpart to the Historical Archives Museum on the other side of the harbour.