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More caves used as air raid shelters - NottinghamThe Caves most recent use was as air-raid shelters during World War II and includes an array of wartime memorabilia. Over 500 high explosive bombs were dropped on Nottingham during May 1941 and over 200 people were killed. Most Nottingham people stayed safe underground, partly thanks to its network of caves.

from Curbed

The urban future is grim, according to this U.S. military training video

Imagine roving bands of child marauders, mazes of squalor extending from high-rises to subterranean networks, and underground slumlords. These are just a few details from the urban future the Pentagon imagines we’ll experience by 2030.

Diamonds _ made of carbon atoms, are the hardest natural substance found on Earth. Formed under extremely high pressure hundreds of miles underground, they are found in very few locations around the world. Diamond is the hardest mineral. Rubies are formed of a mineral called corundum, comprised of aluminum oxide. The red color is caused by traces of chromium. Corundum also forms sapphire in many colors, which generally come from trace mixtures of iron, titanium, & chromium.

Postojna Cave with Train Ride and Predjama Castle Half Day Trip from Ljubljana A unique karst experience of the underground world, a forest of limestone mother nature sculptured. You drive into the cave by a special little train like no where else in the World and then proceed on foot under a guide. You visit the impregnable Predjama Castle that reigns perched high up a vertical cliff.One cannot visit Slovenia without visiting Postonja Cave. The Pivka river has been carving th...

from Ultimate Places

22 Unknown But Awesome Places Around The world

Hallstatt, Austria Hallstatt is one of the best places to visit in the world. It is a medieval village in Austria which lies in the foot of high mountains of Hallstatt. One of the very first underground mines was dug in this place. So, if you want to see mountains, mines, village and snow, this is the place to visit.