Hell door Turkmenistan or "The Door to Hell" is a 230 feet large natural gas hole. On 1971, Soviet geologists were drilling the ground found there was a big cave filled with natural gas. The team decided to break the cave to avoid the poisonous gas leakage and continue digging. They burned the gas and expected that it would be stopped within few days. But unexpectedly the fire is still burning since 1971. The name, "Door to Hell", was given to the field by the locals. The hot spots range over an area with a width of 60 metres and to a depth of about 20 metres.
The Great Wall is one of the greatest wonders of the world. It is winds up and down across deserts, grasslands, mountains and plateaus, stretching approximately 8,851.8 kilometres from east to west of China. Several part of the walls had been built in the 5th century BC. Some of the sections are now in ruins or have disappeared. The great wall was listed as a World Heritage by UNESCO in 1987. The Wall we see today was mostly built during the Ming Dynasty. The Wall has served as a monument of the Chinese nation throughout history.