Aogashima Island, Japan - 青ヶ島 日本 while located in the Philippine Sea, is a volcanic Japanese island. The name Aogashima literally means 'blue island' and is technically part of Tokyo despite being located over 200 miles from central Tokyo.
Explore the ancient caves of Hang Son Doong, Vietnam. Hang Son Doong is one of the largest caves in the world and features a fast-flowing underground river. For spelunkers, exploring Hang Son Doong is the equivalent of scaling Mount Everest.