"This place in Uzbekistan is called by locals "The Door to Hell". It is situated near the small town of Darvaz. The story of this place lasts already for 35 years. Once the geologists were drilling for gas.. Then suddenly during the drilling they have found an underground cavern, it was so big that all the drilling site with all the equipment and camps got deep deep under the ground. None dared to go down there because the cavern was filled with gas. So they ignited it so that no poisonous gas could come out of the hole, and since then, it's burning, already for 35 years without any pause. Nobody knows how many tons of excellent gas has been burned for all those years but it just seems to be infinite there."

http://www.englishrussia.com/?p=1830