Nisyros

Nisyros is a small, near-circular island south of Kos, and it is quite unlike its Dodecanese neighbours: it is a volcano, still active, whose fertile slopes rise to a great collapsed caldera at its centre. Volcanic soil makes the island unexpectedly green, terraced with fig, olive and almond, while the crater at its heart draws day-trippers from Kos for one of the most dramatic short excursions in the Aegean.

The island's port and main town is Mandraki, a tight weave of white and blue houses climbing from the harbour beneath the medieval Knights' castle and the monastery of Panagia Spiliani, which is built into the rock. Its central square, the Ilikiomeni, is shaded by ancient trees and ringed by tavernas, and the town's small volcanological museum sets up the main event inland.

That main event is the caldera itself, a wide bowl nearly four kilometres across, its floor cracked into several craters. The largest and most accessible, Stefanos, is a yellow-streaked hollow some three hundred metres wide that visitors can walk down into, picking their way across a warm, hissing surface of bubbling mud pools and sulphurous fumaroles. It is a genuinely elemental experience, best in the cooler hours before the tour boats arrive.

High on the caldera rim sit two of the prettiest villages in the Dodecanese. Nikia, perched on the southern edge, looks straight down into the crater and gathers around a round, pebble-mosaic square, while nearby Emborios, half-abandoned, has natural steam vents beneath its houses. Down at sea level, the black-and-grey volcanic beaches around Pali and Lies offer swimming in warm, dark-sand coves.

Nisyros has no airport, and most visitors come on day trips by ferry from Kos, with crossings of one to two hours. But staying a night or two, after the excursion crowds have gone, lets you have the caldera and the rim villages almost to yourself and see why this strange, green island lingers so long in the memory.