Hydra is a beautiful Greek island located a couple of hours by catamaran from Athens, right off the east coast of the Peloponnese.
It's proximity to Athens make it a very popular destination since it's conducive to a quick one, or two-day trip.
The whole island consists of a main town, Hydra (Idra), which has a sheltering yacht and fishing boat harbor, along with a couple of other tiny communities, all built on the north coast.
The island of Hydra has been a significant maritime power, and flourished even under the 400 years of Ottoman occupation of Greece. It's shipping families moved merchandise throughout the Mediterranean, and the architecture of the town buildings are a testament to the wealth and prestige its captains brought back home.
Given the long tradition of maritime power, Hydra played a central role in the 1821 Greek revolution that overthrew the Ottoman rulers and led to modern Greece. The most famous admiral from Hydra, and a celebrated hero of the revolution is Andreas Miaoulis, whose statue adorns the entrance to the island's harbor.
For the visitor, Hydra is a trendy destination (many celebrities, like Leonard Cohen maintain a residence in the town), and a quiet place to get away from it all without having to travel to the end of the world. There are plenty of clubs, bars, and restaurants to add some spice to a holiday, but overall, peace and quiet rules in the streets beyond the main promenade around the harbor.
The trademark of the island is the complete absence of automobiles (save for the trash collection vehicle), and everyone gets around of foot or the traditional donkey.
In the summer, several "Flying Dolphins" (catamaran) and ferries bring visitors from Pireas (the port of Athens) to the island. Most of them would stop in a couple of other destinations along the way, Aegina and Poros, so it's possible to perform a mini island-hopping in the Saronic Gulf, right outside Athens.
Several travel agents promote their Hydra-Poros-Aegina trip as a big attraction, and many visitors to Athens find it a convenient way to enjoy a one-day cruise. Most of these cruise ships are of the "tiny" variety, and their amenities and services are more reminiscent of conventional ferry offerings, and do not resemble what most would consider a "cruise ship."
The one-day cruises leave "Flisvos Marina" near Faliro early in the morning and return late in the evening. They are generally very slow, and that leaves only one or two hours in each port. The value of these cruises is quesitionable, so you would be better off to get to these islands with a catamaran. While it is possible to visit Hydra in one day, it would be best to arrange for at least an overnight stay in the island.
Beyond the main town, the other small settlements of the island don't offer many accommodations, with the exception of Mandraki, that's nothing more than an exclusive tourist resort that occupies the island's lone shingle beach. For swimming elsewhere in the island, the modified rocks to the west of the town are the best and most popular spot.
Accommodations are plentiful, but the island is tiny so during the summer it would be best to make reservations ahead of time.