The lake is recognised as a wonder of nature because of its unique appearance and the surroundings.
Arriving at Athens airport you can see down on the ground what looks like a volcanic crater filled with the bluest water. It is called Lake Vouliagmeni and it is a mineral spa that is reported to have many healing properties for ailments such as eczema and dermatological diseases, neuralgia, headaches, disfiguring arthritis, chronic gynaecological diseases, lumbago, sciatica and other problems.

The lake is full of small fish and if you stay still for more than a few seconds they come and feed on your dead cells.
Lake Vouliagmeni (Sunken Lake), a small fresh-water lake fed by underground currents seeping through the mass of Mount Hymettus. It was once a large cavern that collapsed following an earthquake, probably during the early Middle Ages. The outline of the collapsed cavern roof can be clearly discerned from a distance. The lake stands at a 40 cm elevation and its water maintains a constant 24°C year round. It continues deep inside the mountain in an underwater cave never fully explored, as its end seems impossible to trace even by employing sonar detection. Because of its constant and comfortable water temperature, the lake functions as a year-round spa.
The composition of the lake is brackish and full of such minerals as potassium, natrium, lithium, ammonium, calcium, ferrum, chloride and iodine. These minerals are known for giving relief to bone and muscle problems, as well as those listed above. Talking with swimmers of all ages, they say that they have seen an improvement in their health.
The lake is surrounded by beach chairs and umbrellas and there is also a cafe-bar-restaurant. It is excellent for swimming for therapy, as well as for pleasure and there is equipment to assist those who find it difficult or impossible to get into the water on their own. During the summer, Lake Vouliagmeni offers hot-spring baths, hydrotherapy and physiotherapy, and with it lit up in the night, guests of all ages can enjoy swimming until late into the night. In the winter, due to the steady temperature of the healing waters, it is an ideal venue to relax, heal and exercise all at the same time.
The Lake is across the road from the very popular Vouliagmeni beach, one of the best in the vicinity of Athens, and as such, there are many hotels, cafes, bars, tavernas and restaurants in the area.
Diving in the world’s largest submerged cave
In the year 1989 the Greek Ministry of Culture initiated a large-scale cave diving research in the thermal lake of Vouliagmeni near Athens, Greece. The first divers to enter the sump were experienced cave divers Jean-Jacques Bolanz and Luigi Casati. Their discovery was beyond their wildest dreams. They found an entrance to an enormous submerged gallery with crystal clear water. For many years in a row they organised speleological research, being joined by some of the world’s top cave divers. The goal of the 2001 expedition was topographic measurements of the newly discovered parts of the cave and the finalisation of a precise map of this submerged labyrinth. Because of the extreme depths and length of the cave, the use of breathing gas mixtures was essential. The biggest concern was the safety of the participants because seven divers have already lost their lives in this submerged cave, including some American scuba divers from the US airbase which disappeared while exploring the undersea caves; their bodies were found only a few years ago, more than 35 years later!
Cliff Diving World Series
The Vouliagmeni Lake has also played host to the Red Bull Cliff Diving World Series in 2009 and 2011. In 2009, veteran diver Orlando Duque claimed the winning prize, closely beating the young diver Gary Hunt of Southampton who delivered one of the most stunning dives in final rounds of the tournament off a 26 metre high board.