Hydra is one of the Saronic Islands of Greece, located in the Aegean Sea between the Saronic and Argolic Gulfs. It is separated from the Peloponnese by a narrow strip of water. In ancient times, the island was known as Hydrea, a reference to the natural springs on the island. There is one main town on the island,  known simply as "Hydra port". It consists of a crescent-shaped harbor, around which is centered a strand of restaurants, shops, markets, and galleries that cater to tourists and locals. Steep stone streets lead up and outward from the harbor area. Most of the local residences, as well as the hostelries on the island, are located on these streets. Other small villages or hamlets on the island include Mandraki, Kamini, Vlychos, Palamidas, Episkopi, and Molos.

Hydra belongs in a niche group of islands around the world where cars are not allowed. Luckily the island's main attractions are all within walking distance from the port and so are most of its pebbled beaches. Some beaches are accessible by boat, which is fairly inexpensive and easy to find. Alternatively, donkeys are available for transportation with a traditional touch, especially if you want to visit the hilly areas of the island.

Hydra's close proximity to Athens makes it a preferred destination for locals, especially in the weekends. The best time to visit is in late spring – the sea has warmed up to feasible swimming temperatures and locals outnumber tourists – and early autumn, when most of the tourists have departed and the sea is at its warmest.

Hydra is only accessible by fast ferry from Athens (2 hours) as the island is too small to have its own airport. Scheduling a trip there can provide a lot of flexibility as there are several ferries available every day at frequent intervals.