Gruner See in Styria, Austria--Also known as Green Lake, it’s a small body of water in the midst of snow-capped karst peaks and hiking trails, but every spring the surrounding snow melts and turns it into a 30 feet deep lake that’s perfect for diving! Benches, paths, and bridges used by hikers during the winter become submerged and lend an air of adventure and mystery. While the water is around 46 degrees Fahrenheit, the emerald green pool is apparently crystal clear.