The Derweze area is rich in natural gas. While drilling geologists accidentally found an underground cavern filled with natural gas. The ground beneath the drilling rig collapsed, leaving a large hole with a diameter of about 230 ft. To avoid poisonous gas discharge, it was decided to burn the gas. Geologists had hoped the fire would go out in a few days.
That was 40 years ago.
Locals have named the cavern "The Door to Hell".