A tourist peers into the Darvaza Gates Of Hell gas crater in the Karakum Desert, Turkmenistan. The eerie cavern has been on fire for more than 40 years. It was discovered in 1971 by Soviet geologists when the ground beneath their drilling rig suddenly collapsed, leaving a large hole with a diameter of 70 metres (230 ft). As the huge crater was filled with potentially poisonous natural gas the decision was made to set it alight. Scientists expected it to burn itself out within a few days, but the fire is still as fierce as ever.