There's a lake that's a giant sinkhole - Apparently.
Lake Vida, located in Antarctica, is a 15 km² (5.8 sq mi) lake that's actually a giant sinkhole, formed when the ice above it collapsed. It's a rare example of a "closed-basin lake", meaning it has no outlet to the ocean. The lake is estimated to be around 1,200 years old and is thought to be one of the most extreme environments on Earth, with temperatures ranging from -13°C to 0°C (9°F to 32°F) and pH levels as low as 3.5. Scientists have only recently begun to study the lake due to its remote location.