There is a lake just south of the very exclusive resort town of Vouliagmeni, that is not an ordinary lake.
The area was once a mix of small coves and salt flats, but in the Middle Ages an underground cavern collapsed and a shallow lake formed in its wake.
Lake Vouliagmeni, the sunken lake which in Greek is what the name of the place means, is somehow connected to thermals below, so the water stays at 24C all the time.
So now its a spa, and people enjoy swimming in its warm waters every day of the year.
Its also a great place for a tranquil, laid back coffee or meal with friends.
One of those little secrets most tourists pass-by without their knowing.