13. Mausoleum Of Qin Shi Huang, China

Although the Tomb of Emporer Qin Shi Huang was discovered when they found the Terracotta Army in 1974, it has yet to be excavated. This was one of the most important discoveries of all time, but they are nervous that modern technologies could destroy the tomb. 

For these reasons, the Chinese government forbids access to the tomb. All people know is that the mausoleum consists of complex networks and caverns filled with objects the Emporer might need in the afterlife. It is also rumored that there are booby-traps to ward off invaders.