Darvaza, the "Door to Hell"
The rapid program of Soviet industrialization was environmentally costly in many respects; Ulanbataar in Mongolia still bears the scars of its modernization, and the Aral Sea has dried up immensely from the diversion of its waters to sustain cotton fields in Uzbekistan. However, there are much more regionally infamous, exotic examples of problems that arose from often freak accidents and unintended consequences. One such is Darvaza, also known as Derweze. Located in Ahal Province in Turkmenistan, the stench of burning sulfur and the sight of the burning pit is perhaps the most earthly example of the idea of fire and brimstone.
The natural gas pit has been continuously burning since 1971. When the ground beneath the mining operations began to collapse, a large amount of methane gas was being released, posing a potential health crisis for the neighboring residents. The scientists believed it would be less costly to simply burn it off rather than extract it, and they wrongly believed the gas would burn off within a few days.
The village that was Darvaza has been disbanded since 2004 by order of Niyazov -- not out of concerns for the health of the residents, but out of tourism concerns that their nomadic village was an unpleasant sight. Although plans were announced to fill in the pit, it continues to burn even today, and scientists are unsure of when it will cease.