Mount Rushmore and its secret chamber, USA
Apart from the four presidents sculpted in it, Mount Rushmore has its very own secret room. Inside, hidden behind a 1,200-pound granite capstone, the USA’s most important documents are kept safe, including the Declaration of Independence.
Source: Bright Side: https://brightside.me/wonder-curiosities/10-secret-places-hidden-in-plain-sight-336910/
