The sea is bubbling off the pebbly southern shore of Kos, and a small but noisy crowd of people are bathing in a patch of shallow water marked out by stones. What's going on?
We didn't expect to find thermal springs at the end of our hike across the island. As we join the crowd and lower ourselves into the strangely warm seawater, laughing as hot currents mingle with cold, one of the bathers tells us that this coast is volcanic. Waters spill forth at temperatures of up to 60 degrees Celsius.
An idea is planted. Days later, we are boarding a morning ferry for the two-hour crossing to Nisyros, a tiny island that is a sleeping volcano. As part of the Dodecanese islands, Nisyros has been controlled by the Ottomans, the Italians and the Knights of St John, but its character is undeniably Greek. As our boat pulls into Mandraki, the main town (population 600), we check off the icons of Aegean island life: a domed church, waterfront cafes with wooden chairs and moustachioed patrons, blue and white flags, fishing boats and a whitewashed monastery on the hillside.
With no airport, Nisyros is not visited by package tourists. We call in at the first hotel we find on the promenade - it's a family-run place that includes a breakfast of coffee, fruit and yoghurt, and we get a room with a balcony overlooking the water.
On a little beach opposite, we watch a gaggle of white ducks go for a paddle in the sea. The island has little fresh water, so every resident must adapt. An hour later, the sun is stronger and the ducks are taking shade under a beach umbrella.
We've come here for the thermal baths. The hot springs have been used since ancient times. An inscription found in Roman ruins nearby says: 'Happy shall be the man who shall be cured in this way as soon as he passes by the olive gate of the baths of Hippocrates.'