(Middle-Earth coordinates: Mines of Moria) - click to enlarge images.
The closed mine has long tunnels, and a deep natural cave. The excavations dug a huge artificial cave, in which you could fit three 10-story blocks. Marius says: "you can play football inside of them; and you enter there by bus".
2. Top Secret Soviet Underground Submarine Base
Built 126 meters deep underground, the Project 825 also served as a nuclear shelter for 3000 people; it could hold up to nine nuclear submarines at one time; the length of the underground tunnel - half a kilometer, water 9 meters deep.
The cart shown on this photograph was used for transportation of nuclear bombs to the loading area. Next photo - the "Holy of Holies" - Nuclear Weapons Storage Room. Note the reinforced doors (weight 16 tons each):
clipped from: www.darkroastedblend.com 
