Darvaza Crater, Turkmenistan

Also known as The Door to Hell, the Darvaza Crater, is a natural gas crater in the Karakum Black Sands desert, Turkmenistan, about 250 kilometers north of Ashgabat.

It was formed after the collapse of a natural gas field into an underground cavern. According to most sources, it is burning since 1971, when Soviet geologists set it alight to prevent the spread of the potentially poisonous methane gas.
The scientists believed that the gas would extinguish within a few weeks, but it is now still burning.

The Canadian explorer George Kourounis was the first scientist descended into the crater, collecting some extremophile microorganisms that live even in that hellish place.