The 14.4km walk to the top of Mashū-dake (857m) takes you around the lake to its eastern side and back in four to six hours. The pay-off is big: you will be rewarded with amazing volcanic views for much of the hike. The trailhead is at Mashū-ko Viewpoint 1 (400m) at the southern end of the lake; the public bus stops here, though infrequently.