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.
Seattle to Alaska road-trip-alaska.jpg Miles: hours) The last journey is by far (pun intended) the most epic. But don't let this lengthy road (and sea) trip deter you, Seattle to Ketchikan delivers big on both the journey and destination fronts.