Cobalt-blue Tazawa-ko (田沢湖) feels isolated despite being accessible by shinkansen (bullet train). There are some well-serviced beaches, plus a few where you’ll have the natural world to yourself. Some strange creatures from the blue lagoon may have yet to surface – at 423m, Tazawa-ko is Japan’s deepest lake.
The nearby mountains offer excellent views of the lake, and four seasons of activity, including skiing. It's highly recommended to pick up a rental car at Tazawa-ko Station for a night or two to make the most of the lake and nearby Nyūtō Onsen.