The hot springs are another characteristic feature of Nisyros. Hot water wells up at many points along the coast, at temperatures varying from 30 to 61 degrees. The water is a mixture of sea and rain water with the geothermal fluids of the upper hot reservoir. They come to the surface (being hotter and lighter) through the big fractures and faults in the area. They subsequently float higher than the cooler, denser seawater; hence hot springs commonly occur close to the coast.

The best known of the hot springs are those of Loutra, 1500 metres north of Mantraki, and of Thermiani to the north of the village of Pali. Both belong in the class of ‘healing hydro- sulphur salt water springs’.

The spring at Thermiani has been known since ancient times. The inscription found among the ruins of the great archway of the Roman baths which operated in the vicinity -«Ολβιος άνερ ός κατ’ ελάινον ουδόν Ιπποκράτους βαλανείων νοσειρών νόσων ώδ’ έσσεται» ‘Blessed is the man who will be cured by crossing the threshold, made of olive wood, of the baths of Hippocrates, where harmful diseases are washed away’ – supports the view that the father of medicine, Hippocrates, had chosen this spring on Nisyros as a spa. The same spa is probably mentioned by Buondelmonti as healing steam baths.
      Ad trionem in pede montis, contigua maris, spelunca consistit, ad quam circumstantes, doloribus oppressi, accedunt, et, diu morati, in patriam incolumes reventuntur.

On the northern coast, at the foot of the mountain, lies a cave where the ailing come to be cured, stay for a fair length of time and then depart, their health restored.

The most recent period when a spa operated in the region was from 1895 to the beginning of the 1930’s, the celebrated ‘Pantelidi Baths’. The old baths have now been restored, but not returned to use. The temperature of the spring is 33 degrees, but it is expected to rise by 8 to 10 degrees if the water is pumped.

The waters of the hot spring of Loutra have been exploited since 1872 by the Mandraki Public Baths. They are celebrated for their therapeutic properties in the treatment of rheumatism, arthritis, skin complaints and circulatory problems. The spring’s maximum temperature is 46 degrees.

A third well known spring is that in the bay of Avlaki. Its waters were used for therapeutic purposes until the village was abandoned. The hot spring still bubbles up through the sea water; its highest temperature is 61 degrees.

In addition to hot springs, Nisyros is home to several sites where hot steam is produced. Two of these were utilized in the past as natural saunas. The one at Pyria is the main one (and known from the ancient ages). The hot bath chamber and its ancillary buildings are still intact. The other site is at the entrance to the Emporio conurbation. Steam develops a temperature of 34-35°C.