Downhill mountain biking
The gist: using full-suspension bikes designed to float over rocks and tree roots, ‘DH’ bikers race down steep inclines peppered with obstacles.
Where to try it: DH biking Bolivia’s so-called Death Road is one of the nation’s most popular backpacker activities. Somewhat safer is Whistler Bike Park (bike.whistlerblackcomb.com) in Canada, at which winter ski runs morph into summer biking tracks.
Freshwater cave diving
The gist: ocean scuba is extreme enough for some, but descending into a hole in the earth to explore a submerged cave system is next-level stuff. Stalactites are usually the big draw.
Where to try it: Mexico’s Yucatán Peninsula has the world’s largest concentration of cenotes (sinkholes). Fringed by lush jungle, its crystal-clear turquoise pools are idyllic.