Dipping a toe into the Eftalou hot springs on the northern tip of Lesbos island can take what seems like an eternity. Channeled into a superb communal bathhouse at the edge of the azure Aegean Sea, the thermal waters that well up are so sultry — between 109 and 115 degrees Fahrenheit — that visitors tend to slip into the enveloping heat inch by inch.

Greeks have frequented this spot for centuries to soak up the therapeutic properties of the waters, which are rich with radium, chloride, sodium and other minerals said to ease arthritis and rheumatism. While Lesbos, as a volcanic island, has a number of natural thermal springs, Eftalou holds a unique perch next to a tranquil pebble beach with wind-sculpted lava formations.

Visiting is easy from the nearby town of Molyvos, adorned with pretty stone houses set into the side of a steep hill and crowned by an old Genovese castle. After walking or taking a bus to the entrance to Eftalou, a path leads to a domed, whitewashed building where the communal hot bath is next to a more modern facility, where visitors can rent private bath tubs.

Eftalou’s ritualistic endurance challenge involves soaking for a few minutes, or as long as you can stand it, then plunging directly into the bracing waters of the Aegean, and heading back to the thermal pool. The relaxation sets in after a few rounds, deepened by floating in the salty sea and looking across the horizon toward the purple mountains of Turkey, or gazing upward at the impossibly blue sky.

When you’re done pampering yourself, it’s a short walk around a bend toward curving Golden Beach, where the waves might lull you into a peaceful nap, if you don’t give into the urge to snorkel. The nearby Eftalou Taverna serves excellent fried, stuffed zucchini flowers and fresh seafood. There you can sit as the orange sun sinks into the Aegean, and the lava rocks formed at the birth of the island cast shadows on the warm beach.

LIZ ALDERMAN

Read more about thermal springs The New York Times