Hikers that ascend to the summit of Mount Fuji, Japan, can visit the caldera, since the mountain is actually an active volcano. At 12,380 feet, Mount Fuji is the highest mountain in Japan, as well as its most popular tourist attraction, with more than 200,000 people making the hike to the summit every year. (U.S. Air Force photo illustration by Tech. Sgt. Christopher Marasky/Released)