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.
See Baatara Gorge Waterfall's three natural bridges
The Baatara gorge waterfall (also known as the “Cave of the Three Bridges”) in Tannourine, Lebanon. The waterfall drops 255 metres ft) into the Baatara Pothole, a cave of Jurassic limestone located on the Lebanon Mountain Trail.
In pictures: Inside Hang Son Doong, the world's largest caves in Vietnam
Cave of the Crystals or Giant Crystal Cave is a cave connected to the Naica Mine 300 metres ft) below the surface, in Naica, Chihuahua, Mexico. The main chamber contains giant selenite crystals (gypsum, some of the largest natural crystals ever found.
Fingal’s Cave, Inner Hebrides, Scotland. "Fingal's Cave is a sea cave on the uninhabited island of Staffa, in the Inner Hebrides of Scotland, part of a National Nature Reserve owned by the National Trust for Scotland" via Wikipedia.
Salt: Santa barbara salt caves for relaxation, inspiration and pleasure. Cool rooms underground, with ceilings, walls and floor made of salt! Luminous, tranquil and grounding: Check it out if you're in downtown Santa Barbara!