Mount Aso, located in central Kyushu, has the world's largest volcanic caldera with a circumference of about 120 kilometers (about 75 miles), and is also the largest active volcano in Japan. Inside the caldera are five volcanic peaks, including Nakadake which is still active and regularly emits smoke and ash. Much of the landscape inside the caldera is grassy and green, and the highest point is just under 1,600 meters.

Mt Aso is an easy day trip or overnight from Beppu.