Nisyros (Greek: Νίσυρος; also transliterated Nissiros; see also List of traditional Greek place names) is a volcanic Greek island located in the Aegean Sea. It is part of the Dodecanese group of islands, situated between the islands of Kos and Tilos. Its shape is approximately round, with a diameter of about 8 km, and an area of 41.6 km². Several other islets are found in the direct vicinity of Nisyros, the largest of which is Gyali. The island has a mountainous interior and in its center several craters are found. Its coasts are generally rocky or pebbled, but there are also a few sandy beaches (mainly in the northeastern part).
The volcano is currently active (not erupting), and fumaroles are found at the craters. The latest eruptive activity was a steam explosion in 1888, after small ash eruptions in 1871 and 1873 and earthquakes are not infrequent. A period of seismic unrest in 1996-1997 led an international team of scientist to initiate monitoring of the volcanic unrest in the European-Union sponsored Geowarn project. The entire volcanic complex includes the seafloor between Nisyros and Kos, the island of Gyali, and a part of Kos island.
According to Greek mythology, the island was formed when Poseidon cut off a part of Kos and threw it onto the giant Polyvotis to stop him from escaping. The ancient name of the Nisyros was Porphyris. Ancient walls, dating from the 5th century BC, part of the acropolis of the island, are found near Mandraki.
It was apparently also a source of millstones
used in some of the earliest watermills, being referred to by epigrammatist
Antipater of Thessalonica in the 1st century BC.
The main town and port of the island is Mandraki. Other villages are Paloi, Nikeia and Emporios. According to a 2001 census, the resident population is 938, although in summer it is augmented by many tourists as well as expatriate Nisyrians who visit the island for their vacations. Tourism is not so heavily developed as on other Greek islands. Deposits of perlite and pumice on Gyali provide much of the wealth of the island. The island used to be self-sufficient, and many crops were grown on its terraced slopes. Today, though, they are cultivated on a smaller scale.
The island is reachable by ship from Pireaus and Kos, and in summer, there are many daily trips from the village of Kardamena on Kos. There is also a heliport.
A health spa with sulphurous waters East of Paloi used to be world-famous in the first decades of the 20th century.
A traditional product of Nisyros is soumada, a non-alcoholic almond-flavoured drink.
The patron saint of the island is Saint Nikitas. Many Orthodox Christian churches are found on the island, as well as four monasteries which are not inhabited by monks today, although various celebrations take place in them. The largest monastery is the one of Panagia Spiliani (Blessed Virgin Mary of the cave) at Mandraki. It is built beside the medieval castle erected by the Knights Hospitaller who conquered the island in 1315.