There's a lake that turns into a giant ice circle every winter - Apparently.
Lake Saimaa in Finland, a large lake with over 4,000 islands, experiences a unique phenomenon where its surface freezes into a circular shape due to the shape of its basin. This occurs every winter when the lake's surface temperature drops to around -20°C (-4°F). The lake's ice circle can be up to 400 meters (1,312 feet) in diameter, making it one of the largest and most fascinating natural ice formations in the world. This phenomenon has been observed and documented by scientists and locals for centuries.