Kussharoko Lake in Teshikaga-cho, Hokkaido, is the largest caldera lake in the entire country, and it is said that 80% of the clear, beautiful water is natural spring water. In summer, the area bustles with people enjoying camping and water sports, and when winter comes around, visitors can see any number of swans gathered on the water and by the shores. Several observation decks stand in the surroundings as well, allowing visitors to enjoy the vast lake from a variety of viewpoints: the Tsubetsutoge Observation Platform, which has an altitude of 947 meters; a huge panorama spreads out in front of the Bihorotoge Observation Platform; and the Mashuko Third Observation Platform, from which visitors can gaze out at both Mashuko Lake and Kussharoko Lake. If the weather conditions are just right, a sea of clouds will appear over the water of Kussharoko Lake, creating a stunning scene that can be seen from any one of the observation decks. The best timing to see the sea of clouds is in early mornings between June and October, in particular just as the sun begins to rise.