In the Central Asian nation of Turkmenistan, there is a man-made crater known as the Door to Hell that is full of man-made fire and fueled by natural gas. Soviet engineers purposefully lit the fire in 1971 after a brief natural gas excavation effort ended with a massive collapse, which created the crater. The crater is more than 200 feet in diameter, and as of 2015, the fire is still burning.
The decision to light the fire was mostly driven by safety concerns, with scientists fearing that the gas field could contain dangerous gasses. At the time, the engineers believed that the fire would only burn for a month or so at most before running out of fuel and naturally dying out.
Though the Turkmenistani president announced plans to close the crater in 2010, it was still open in 2014. During this year, National Geographic sponsored an exhibition to the crater, during which an explorer collected soil samples from the bottom of the crater. These samples showed that there is microbial life inside the crater.