The Aso Caldera is one of the largest in the world (25km north–south) and the Panorama Line traces its crater rim and the active Nakadake summit cone. From Aso city up Daikanbo on the northern outer rim, west along the Milk Road, then up to the active crater of Mt Aso (access depends on volcanic alert level), through the Kusasenri grasslands, and finishing at Takamori in the southern caldera. Iconic Kyushu touring — locals call it Japan's Best Ride.
Clone it to your planner, customize dates and stops, then ride. All free.