Photo: Ryan Deboodt, Oxalis.com.vn
The Place: Son Doong Cave; Phong Nha-Kè Bàng National Park, Vietnam
The Reason to Go: Possibly the largest cave in the world, Son Doong can fit a flying Boeing 747 in its largest section and is home to a jungle filled with 100-foot-tall trees, massive 260-foot stalactites and even its own climate. But the trek to get there isn't for someone who circles a parking lot to find a spot close to the storefront. Son Doong Cave is part of a network of recently discovered monumental caverns in Phong Nha-Ke Bang National Park, and it requires (among other things) roping across a river, climbing massive slick boulders and scaling up a 200-foot wall to reach it.