Lake Hévíz (There are only two lakes in the world which water is warm in winter too. One of them is in New Zeland and the other is this lake in Hévíz, Hungary. It is the biggest hot water "spa-lake" in Europe.)
Danubius Health Spa Resort Hévíz - Lake Hévíz
Nature has bestowed beauty in plenty on Lake Hévíz. The most beautiful parts of the landscape around Lake Hévíz were formed by volcanic action, and even 2.5 million years after the extinction of the volcanoes their effect, though tamed, can still be felt. Dozens of sulphuric and carbonated springs burst from the ground along the lakeside, and in most of them people have sought (and found) healing for centuries.