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.
The Great Blue Hole is the most popular dive destination in Belize. This massive hole under the water is near the Lighthouse Reef and creates a perfect circle of deep blue water. The water is 407 feet deep. It's breathtaking.
Fingal's Cave is a sea cave on the uninhabited island of Staffa, in the Inner Hebrides of Scotland, known for its natural acoustics. The National Trust for Scotland owns the cave as part of a National Nature Reserve.