Want to know what it would be like to live in a subterranean world? Visit these incredible old mines and see how the Morlocks live.
Turda Salt Mine (Salina Turda), Romania, operated between the 2nd century, abandoned in 1932, reopened for tourists in 1992.
More than three billion tons of salt was mined here. One of its halls named Rudolf hall is 260 ft (80 m) long, 160 ft (50 m) wide and 130 ft (40 m) high.
The 178 mi (287 km) long Wieliczka salt mine, Wieliczka, Poland, built in the 13th century, but some parts operated until 2007. There are three chapels, dozens of statues and some chandeliers made of salt, among others.
Blegny-Mine, a coal mine in the Liège region of Belgium, dates back to the 16th century. The visitors could walk 200 ft (60 m) under the earth with a former miner and discover the process of coal mining.
The salt mine of Praid, Romania, used since the Dacian times, now one of Europe's largest salt mines
The second largest salt mine in the world, the Khewra Mine, (also known as Mayo Salt Mine), in Khewra, Pakistan, supposedly discovered by the troops of Alexander the Great, but the main tunnel was only built in 1872. And there is a salt mosque!
The Bonne Terre lead mines in Missouri, used between 1860 and 1962. After the pumps were turned off, groundwater began pouring in, and slowly flooded the most of these man-made caverns. Now it's the world's largest freshwater dive location with 24 paths.
The two upper levels are lighted and accessible via guided walking tours, but the lower three are underwater. Visitors could see some drowned equipment here.