Spectacular but woefully underappreciated natural wonders are tucked away all over the planet. Granted, visiting some of them might leave you sweaty, faint, and gasping for breath.

Hardly anyone goes to see Turkmenistan’s Door to Hell, for instance, even though it offers the rare chance to see a giant fire-filled pit in the middle of a barren desert. The origins of the crater are a bit mysterious, but the most-told version has Soviet geologists igniting a natural gas seep in 1971 after an oil rig collapsed into the ground. The pit has been burning ever since.

During a 2013 expedition funded in part by the National Geographic Society, George Kourounis became the first—and, so far, only—person to don a silvery flame-resistant