Hell Gate

Its called by locals Door to Hell, this place in Uzbekistan is located near the small town Darvaz. The fire that burns inside the hole will continue to remain lit even if drenched by rain water. When the geologists who do drilling for gas, 35 years ago, suddenly they found an underground cavern is so big.
No one dared to go there because the cave was filled with gas, so they lit it so that no poisonous gas could come out of the hole, and since then, has been on fire. No one knows how many tons of excellent gas is burned for years, but it seems to be unlimited.