Lake Kussharo, located in Akan National Park in Hokkaido, Japan, is a massive caldera lake known for freezing over completely in winter. Its central island, Nakajima, is a stratovolcano and the largest recursive island in Japan. The lake's acidic waters support few fish, but rainbow trout have been introduced.. You can enjoy swiming in the lake as the water is very clear. Visitors can enjoy outdoor hot springs along the shore. Not only a public wild hot spring, there are spots where you can make your own tub digging the shore. With its unique features and stunning natural beauty, Lake Kussharo is a must-visit destination for nature lovers and adventure seekers alike.