Built in the early 1940's, the Wrights Hill Fortress is a circular artillery embankment that consists mostly of long underground tunnels which were actually used to create the sound of the dwarven mines of Middle Earth.

Completed in the final years of World War II, the fort was meant to have three large guns positioned on the above ground portion, although only two (9.2" Mk. XV's for you armaments fans out there) were ever installed. The squat circular base was not much to look at above ground, but below ground it contained a labyrinth of tight concrete tunnels, some buried as deep as 50 feet deep in the earth. Most of the space underground was used as storage or office space, although there were also rooms filled with large diesel engines for power.

The base never saw any action during the war, but both of the massive guns were fired in the years following the cessation of hostilities. The test fires shot projectiles out over the New Zealand territory seemingly just to say that they hadn't been put in place for nothing. Although their existence really did end up amounting to little as they were scrapped in 1960, with the parts being sold to the Japanese, possibly as a way of saying, "here we built these guns for you anyway." The fort was abandoned not long after. 

Today the fortress has been restored by a preservation society and officially named a historic landmark. On certain holidays the 2,000 some feet of tunnels are opened to visitors. The site is also often used as a set for televisions and film productions. Famously the tunnels beneath the base were used as an audio palette for the Mines of Moria in Peter Jackson's Fellowship of the Ring. Creating tunnels 50 feet underground might not be deep enough to unleash a Balrog, but it is deep enough to sound like you could.