Lake Vouliagmeni, nestled in the Athenian Riviera, is one of Greece's 20 hot springs. Geologists believe it formed around 2,000 years ago when a cave roof collapsed. The lake holds a fascinating cave system, though it's off-limits to the public due to safety concerns. Remarkably, it's also the starting point for the world's longest underground tunnel, measuring 800 meters in length and reaching a depth of 80 meters. The lake's brackish water is continually refreshed by the sea and thermal springs, making it a geological wonder of global significance. The warm water, ranging from 21°C to 29°C, provides a natural thermal spa experience, renowned for its healing properties. The lake is well-known for its capacity to provide relief from rheumatic and gynecological issues, and it is an excellent place to relax and rejuvenate the body and spirit. Surrounded by imposing rock formations that change color throughout the day, the lake is an ideal spot to enjoy this romantic landscape. Visitors can appreciate this view from the lakeside coffee restaurant, which is open all day and into the evening.