Situated in the Tohoku region across the prefectures Aomori, Akita and Iwate you'll find the great Towada-Hachimantai National Park. Lake Towada, Japan's deepest lake, and Oirase Valley are part of this wonderful area, particularly interesting in autumn. However, if you love the snow, take a winter trip like me. At the traditional Tsuta Onsen Ryokan (in Japanese) I got some snowshoes and went to explore the nearby forest and a couple of other small lakes.
Find out more about Lake Towada.