Door to Hell, Turkmenistan
Soviet geologists started the fire that burns in the Door to Hell in 1971 after accidentally discovering a cave full of natural gas. They sparked the decades-old inferno as a precautionary measure, meant to keep the gas from leaking out and killing the locals. The blaze was expected to fizzle after a few days, but burns to this day, creating spectacularly sci-fi views for those willing to trek to the middle of the Karakum Desert. The Door to Hell is in the village of Darwaza about about 150 miles from Ashgabat, so make sure you leave in time to make it there by dusk, when the view is particularly striking.