Mandraki

Mandraki is the capital and main harbour of Nisyros, a small volcanic island in the Dodecanese, and by far its largest settlement, with a population of 791 as recorded in the 2021 census. Whitewashed houses climb the slope above the port in the pattern typical of the islands, their flat roofs and narrow lanes largely unchanged by the tourism that now supports the local economy alongside fishing.

The Castle of the Knights and the Monastery in the Rock

A fortress dating to 1315, built during the era of the Knights of St John, still looks down over the town, a reminder that Nisyros's position between Kos, Tilos, and Astypalaia mattered long before it became a stop for day-trippers. Most visitors arrive the same way locals always have — by boat, since the island has never had an airport — with ferries and catamarans linking Mandraki to Kos and Rhodes.

Set into the same rock as the castle is the Monastery of Panagia Spiliani, the religious centre of the island, reached by a stepped lane climbing out of the village and built around a cave sanctuary; it is the focus of the biggest religious festival in the local calendar each August. Directly below the monastery rock the shore drops into Hochlaki, a beach of large, smooth black volcanic pebbles with no sand at all, a striking piece of geology that also explains why swimming there takes a little care whenever there is any swell running.

Paleokastro and the Ancient City

The most impressive thing at Mandraki is not medieval at all. A short, steep climb above the village brings you to Paleokastro, the acropolis of the ancient city of Nisyros, whose surviving wall is dated to the 4th century BC and whose earliest phases reach back to the sixth. It is built of enormous black volcanic slabs, some of them 3.5 metres across and weighing three to four tonnes, laid without mortar in the massive polygonal masonry loosely called cyclopean. Wall and cliff together enclose an area of roughly 130,000 square metres with a perimeter approaching two kilometres, and the circuit is generally reckoned among the best-preserved ancient fortifications anywhere in the Aegean. The line of the wall ran north to the rock where the Knights later put their castle and where the monastery stands today, the same defensible high ground reused across two thousand years.

Living on the Rim of a Volcano

Nisyros is a stratovolcano, and the island is essentially its cone. The caldera at the centre is three to four kilometres wide, and the landscape as it stands has been assembled over roughly the last 150,000 years through three main eruptive stages. Inside it sits Stefanos, one of the largest phreatic craters on earth, about 330 metres across and 27 metres deep, with a flat floor visitors can walk down onto: the ground is warm underfoot, stained yellow with sulphur and hissing with steam vents. The neighbouring Polyvotis crater has boiling mud pools and fumaroles running above 100°C. The last eruption was a steam explosion in September 1888, and while the volcano is classed as active rather than erupting, the hydrothermal system beneath it has never switched off. In October 2025 the island was admitted to the UNESCO Global Geoparks Network as the tenth Greek site to join.

Greek myth had an explanation for all of this long before geology did. In the war between the gods and the giants, Poseidon is said to have torn off a piece of Kos and hurled it down onto the giant Polybotes to pin him in place; the island is the rock, and the giant is still underneath it. The name of the Polyvotis crater comes straight out of that story.

The Rest of the Island

Nisyros is small — the main island covers about 41.6 square kilometres, and the municipality, islets included, counted 1,048 residents at the 2021 census — but it is anything but flat. Profitis Ilias, on the caldera rim, reaches 698 metres. Beyond Mandraki there is the fishing harbour of Paloi, and two villages perched on the rim, Emporeios and Nikia, both now down to a few dozen permanent residents and both looking straight into the crater. About a kilometre and a half east of Mandraki, the thermal spa at Loutra draws water at around 37°C that has been used for rheumatic and skin complaints since antiquity. Offshore lies the islet of Gyali, whose white pumice quarries are visible from the coast and which makes a common short boat trip for swimming.

A Harbour Worth the Detour

Ferries and catamarans run from Kos and Rhodes through the season, with day boats out of Kardamena on Kos crossing most summer mornings and returning in the afternoon — enough time for the volcano and a meal on the waterfront, and not much more. Staying the night, or arriving on your own keel, is what separates a look at Nisyros from actually seeing it.

The harbour itself offers reasonable shelter and the services a yacht needs for a short stay, making Mandraki a natural base for exploring the rest of the island, including its dormant volcanic crater further inland. It's precisely this mix of easy access and old-fashioned charm that makes it worth a visit if you're chartering a gulet in Greece.