The Door To Hell
The “Door to Hell” (also known as the Gate to Hell, the Crater of Fire, Darvaza Crater) is a natural gas field in Derweze, Turkmenistan, that collapsed into an underground cavern in 1971, becoming a natural gas crater.  Geologists set it on fire to prevent the spread of methane gas, and it has been burning continuously since then. The diameter of the crater is 69 metres (226 ft), and its depth is 30 metres (98 ft).
The crater is a popular tourist attraction. In the past five years 50,000 tourists have visited the site. The gas crater has a total area of 5,350 m2, the size of an American football field. The surrounding area is also popular for wild desert camping.
The site was identified by Soviet engineers in 1971. It was originally thought to be a substantial oil field site. The engineers set up a drilling rig and operations to assess the quantity of oil available at the site. Soon after the preliminary survey found a natural gas pocket, the ground beneath the drilling rig and camp collapsed into a wide crater and was buried.
Expecting dangerous releases of poisonous gases from the cavern into nearby towns, the engineers thought it best to burn the gas off. It was estimated that the gas would burn out within a few weeks, but it has instead continued to burn for more than four decades.
The crater was featured in a Die Trying episode titled “Crater of Fire”. Explorer George Kourounis became the first person to ever set foot at the bottom, gathering samples of extremophile microorganisms. The episode was broadcast on the National Geographic Channel on July 16, 2014.