Lake Vouliagmeni

Lake Vouliagmeni lies about 25 kilometres south of Athens on the Saronic Gulf, a natural brackish lake formed roughly 2,000 years ago when the roof of an underground cave system collapsed. Fed from the depths (over 100 metres - the true bottom is not mapped), the lake holds thermal water of 22-29 degrees Celsius year round, mixed from sea and freshwater springs. Its mineral content - sulphur, lithium, sodium - has long been considered therapeutic for rheumatism and skin conditions. Today the lake is protected as a Natura 2000 site and natural landmark; for an admission fee you can swim year round, while small fish nibble dead skin from bathers' feet. An attached underwater cave was explored by divers in 1991 and remains off-limits to tourism.