In the middle of the Karakum desert a hole seventy metres wide has been burning without pause for half a century: a Soviet drilling rig collapsed into a gas pocket and someone set it alight, assuming it would burn out in days. By daylight it is a smoking pit and not much more; after dark it becomes a bowl of orange flame visible for kilometres. You get there by four-wheel drive and camp on the rim, because that is the only way to see it properly.