The waterfront of Hydra (ÍDHRA TOWN) is lined with mansions, most of them built during the eighteenth century, on the accumulated wealth of a remarkable merchant fleet of 160 ships which traded as far afield as America and, during the Napoleonic Wars, broke the British blockade to sell grain to France. Fortunes were made and the island also enjoyed a special relationship with the Turkish Porte, governing itself and paying no tax, but providing sailors for the sultan's navy. These conditions naturally attracted Greek immigrants from the less-privileged mainland, and by the 1820s the town's population was nearly 20,000 - an incredible figure when you reflect that today it is under 3000. During the War of Independence, Hydriot merchants provided many of the ships for the Greek forces and consequently many of the commanders.

The mansions (arhóndika) of these merchant families, designed by Venetian and Genoese architects, are still the great monuments of the town. A town map is available locally, if you are interested in seeking them out - some are labelled at the entrance with "Oikía" (home) and the family name. On the western waterfront, and the hill behind, are the Voulgaris mansion, with its interesting interior, and the Tombazis mansion, used as a holiday hostel for arts students. Set among pines above the restored windmill on the western point, the Koundouriotis mansion was the home of George Koundouriotis, a wealthy shipowner who fought in the War of Independence and whose great grandson, Pavlos Koundouriotis, was president of republican Greece in the 1920s. It is being refurbished as a museum with EU funding. On the eastern waterfront are the Kriezis mansion, the Spiliopoulos mansion and the Tsamados mansion - now the national merchant navy college which you can sometimes visit between lectures. The historical archives museum is also on the eastern waterfront.

Ídhra is also reputedly hallowed by no fewer than 365 churches - a total claimed by many a Greek island, but here with some justice. The most important is the church of Panayía Mitropóleos, set in a monastic courtyard by the port, with a distinctive clocktower and a Byzantine museum of uncertain opening hours.