What is Therma, and why every Ikarian knows it

A few kilometers north of Agios Kirykos, where the road climbs gently toward the island’s northern coast, lies Therma — a small, quiet village that has lent its name to one of Greece’s rarest natural phenomena: its thermal springs, known for centuries for their therapeutic properties. If you’re staying at Kastro Hotel in Agios Kirykos, Therma is just a few minutes away by car, making it an easy half-day trip for anyone who wants to see something beyond beaches and hiking trails.

A history spanning centuries: from antiquity to today

The therapeutic use of Therma’s springs is documented as far back as the 4th century BC, when people traveled from across Greece and Asia Minor to visit the organized bath facilities of the ancient town, located about 300 meters east of today’s village, where ruins of the acropolis and baths still survive, according to historical records. Their use continued through the Byzantine era, when baths were built for the royal family, and later during Ottoman rule, when local elders made use of them. After Ikaria’s union with Greece in 1912, development of the springs picked up again: throughout the 1920s several hotels and bathing enterprises opened, operating until the early 1940s, when the war and its difficult aftermath temporarily halted them.

The radon that makes them unique

According to research conducted by Greek universities, Ikaria’s thermal springs have among the highest radon concentrations in Greece and rank among the most radioactive springs in the world. Water temperature ranges from 31°C to 58°C depending on the spring — from Artemis, the hottest and most radioactive at 50.4°C, to Apollo and Mustafa-Litsa. Many researchers have linked the island’s longevity, which has placed it among the world’s five Blue Zones, to residents’ long-term exposure to this mild, natural radon — though the connection remains an open question for further scientific study and should not be read as medical advice.

How to visit the springs today

The municipal bath center in Therma operates mainly during the summer months, usually for a small entrance fee, and offers organized facilities for guided hydrotherapy — traditionally associated with rheumatic, gynecological, and skin conditions. Because opening hours change from year to year, it’s worth asking locally before heading down. Beyond the organized center, smaller, wilder springs bubble up closer to the sea, where the hot water meets the waves — an experience many visitors remember more vividly than any beach on the island. Wear something you don’t mind getting slightly stained, as the water leaves a distinctive color on the rocks.

Where to stay to explore them

Therma is close enough to Agios Kirykos that you can visit it as a day trip without changing where you’re staying. If you’re wondering more broadly where to base yourself on the island depending on your interests, see our complete guide by area. At Kastro Hotel you’re just minutes from Agios Kirykos, with easy access to Therma, quiet surroundings, and Aegean views. You can check availability and book directly through our official booking page.