Video of a burning gas crater in Darvaza, Turkmenistan. Locals call it Door to Hell or Gates of Hell.
The diameter of the crater is about 60 metres, and its depth around 20 metres. It has been burning continuously for the past few decades.
The phenomenon is not all natural though. There are a few versions of the event, but in general a failed gas exploration caused the ground to collapse in the 1960’s or 1970’s. The engineers set the place on fire to prevent poisonous gas from leaking to nearby towns, which was a logical decision at that point.
They probably expected the gas to burn out within a few weeks, but it’s been on fire after all these years. Thanks to the accidental “effort”, the place becomes a spectacular attraction for travellers nowadays.