In the twilight days of the Cold War, the Soviets began building UNK, a proton accelerator in the town of Provtino that would have been the biggest in the world. It was never completed...but its ghostly remains are still there.

The photo up top shows the vast underground tunnels the Soviets were building for UNK - it actually wasn't necessary to build the tunnels that big, but all the builders had available was subway construction equipment. For more incredible photos of the above ground construction site and the abandoned tunnels underneath, check out English Russia, and check out Discovery News for more on the site's history.