If Hokkaido were a cheese, it would be Swiss, so riddled is it with crater lakes. The fairest of them all is Lake Mashu, a 211-meter-deep (692-foot-deep) volcanic lake that some claim has the clearest water in the world. The lake retains its clear blue hue and remarkable underwater visibility of up to 41 meters (135 feet) due to the fact that no rivers empty into it. Fog and mist are common and add to the mystery. But when the mist clears and you take in the scene from one of the viewing platforms that ring the lake, you’ll be treated to one of the most spectacular vistas imaginable.