While drilling in 1971, Soviet geologists tapped into a cavern filled with natural gas. The ground beneath the drilling rig collapsed, leaving a large hole with a diameter of 70m. To avoid poisonous gas discharge, it was decided the best solution was to burn it off. Geologists had hoped the fire would use all the fuel in a matter of days, but the gas is still burning today. Locals have dubbed the cavern “The Door to Hell”. Continue reading for more.