A whiff of sulphur sometimes drifts as far as the ship's deck when the anchor drops off Mandraki. Nisyros, in the Dodecanese, is an island born of a volcano that is still active, although not in the form of eruptions: here, the earth smokes, rumbles gently and colours the landscape in ochre and white. Opposite, the islet of Gyali, where pumice is quarried, whitens the horizon like a dune set on the water. Ships anchor offshore and tenders drop passengers at the small port of Mandraki, the island's main town, where cube-shaped houses with blue shutters and pebble-paved lanes set the tone for a day out of the ordinary.

Mandraki, a village built on lava

The first minutes are spent wandering through the village's maze. The houses, built of volcanic stone and insulated with pumice, line lanes too narrow for cars. Wooden balconies overflow with bougainvillea, cats doze on the steps and the cafés on the main square serve soumada, a local almond drink found almost nowhere else.

Panagia Spiliani, the monastery in the cave

At the top of the rock overlooking the port, the Panagia Spiliani monastery occupies a natural cavity transformed into a sanctuary. It is reached by a staircase of about 270 steps; the effort is rewarded with a plunging view over the flat roofs of Mandraki and the Aegean Sea. Just below, the remains of the Paleokastro, an ancient acropolis with Cyclopean walls of black basalt, recall that the island was already inhabited more than two thousand years ago.

Descending into the Stefanos crater

The highlight of the port call lies in the centre of the island, about a twenty-minute drive from the port. Shuttles and organized excursions take passengers to the edge of the caldera, 3 to 4 km wide, where the Stefanos crater opens up: a lunar amphitheatre about 300 m in diameter, into which a path lets you descend. At the bottom, fumaroles hiss, mud bubbles in places and the hot ground gives off the characteristic rotten-egg smell of sulphur. Walking in an active crater, surrounded by yellow and white walls, provides a sensation that few Mediterranean ports of call can offer. Good shoes and water are a must; there is no shade.

Nikia and Emporios, balconies over the caldera

On the ridge surrounding the volcano, two tiny villages compete for the finest viewpoints. Nikia, with its oval square paved with pebble mosaics and its small volcanology museum, overlooks the crater on the south side. Emporios, long abandoned, is slowly coming back to life; a path there leads to a cave naturally heated by steam, a free sauna courtesy of geology. Some excursions combine the volcano with one of these villages.

A swim before re-embarking

Back toward the coast, the remaining time is ideal for swimming. Chochlakia beach, behind the monastery, lines up black pebbles polished by the waves; those of Lies and Pachia Ammos, farther along the north coast, offer dark sand and crystal-clear waters. The coastal hamlet of Paloi, a former fishermen's refuge, lines up a few tavernas where octopus dries in the sun in front of the boats. 1.5 km east of the port, the Loutra baths have used, since the 19th century, hot springs that gush naturally at around 37 degrees.

Boarding the tender again, you take one last look at this smoking rock set on the sea. Nisyros is like no other Greek island: no famous ruins or nightlife, but a direct encounter with the forces that shaped the Mediterranean. Long afterward, a whiff of sulphur or a basalt wall is all it takes to think of it again.