The mountainous prefecture of Nagano is the perfect summer resort to avoid the heat, with the town of Karuizawa being one of the most popular summer getaway spots in Japan.
Take advantage of the relatively cool weather to explore the famous Matsumoto Castle, one of Japan's oldest shrines in Suwa Taisha, and Zenko-ji, a major pilgrimage site. Nagano's many tall mountains serve as challenging but beautiful hiking trails, especially those of Kamikochi.
That being said, Nagano is also a great destination in the winter, and it was the host of the 1998 Winter Olympics. The prefecture's mountains are some of the largest ski resorts in Japan, most notably Shika Kogen and Mount Hakuba. After being out in the cold, seek warmth in one of Nagano's many famous hot springs.