Dunno if this is a repost, but this is a large crater located near the village of Derweze, Turkmenistan formed from a large cavern underground due to excavating by geologists years back. As they dug deeper, they found more and more gases. Eventually the equipment was lost and they abandoned it, and because of the apparent dangers, no one would dare go in there. So they decided to ignite it in hopes that none of the poisonous gases would come out of there. It's been continuously on fire for almost 36 years now, and even to this very day, as we speak, it's still burning. Most of this is due to the rich sources of natural gases coming the out of areas where they drilled. Scientists don't know much has been burned throughout the years, but it's pretty much infinite if it's been ablaze for that long. The locals have appropriately named it "The Door to Hell".