Burn O'Vat is a cool glacial pothole in Aberdeenshire, Scotland that was formed thousands of years ago by melting ice. It's like a natural amphitheater with a deep bowl and a narrow entrance. People have been visiting it since Victorian times, and there's even a legend that a Scottish outlaw once hid out there.
The walk out to the pothole (about 1.5 hours) offers some awesome views of the countryside.