Mount Fuji might get all of the press, but the largest active volcano in Japan is actually Mount Aso, located in the center of Kumamoto Prefecture on the southern island of Kyushu. Mount Aso can also claim the world's largest caldera, a cauldron-like area of land that is formed after the collapse of a volcano following its eruption. While the massive eruption that formed the Aso caldera occurred at least 100,000 years ago, today's Mount Aso is still an active volcano, becoming increasingly productive since the end of 2014 as it spews out clouds of smoke and ash daily. Previously, visitors were permitted to peer over the edge of the bubbling Nakadake crater, the last of the five main peaks to be active. Today, a two-kilometer restriction is in place and looks to remain so for the foreseeable future. Still, most days you can drive up to the parking area on the volcano's wide apex and watch Mount Aso in all of its glory.