Lonely Planet review
The Five Mountains of Aso are the smaller mountains within the outer rim: Eboshi-dake (1337m), Kijima-dake (1321m), Naka-dake (1506m), Neko-dake (1408m), furthest east, and the highest, Taka-dake (1592m).
Naka-dake is the active volcano: very active in recent years, with fatal eruptions occurring in 1958 and 1979, and other significant eruptions in 1989, 1990 and 1993.
If Naka-dake is behaving, a cable car whisks you up to the crater's edge in just four minutes, or it's ¥600 in tolls and parking if driving yourself. The cable car is 3km from the Aso Volcano Museum. From there, the walk to the top takes less than 30 minutes. The 100m-deep crater, with pale green waters bubbling and steaming below, varies in width from 400m to 1100m, and there's a walk around the southern edge of the crater rim. Arrive early in the morning to glimpse a sea of clouds hovering inside the crater, with Kujū-san (1787m) on the horizon.