6. Iron Mountain, Michigan, USA
Media Source: mentalfloss.com
The retired limestone mines placed under Iron Mountain have 1.7 million square feet worth of vaults. These vaults are popular for keeping one of the most important documents, recordings, photo negatives, and original film reels such as the remains of Flight 93, the original photo of Einstein sticking out his tongue and Edison’s patent for the light bulb. The entrance is protected by two waves of guards. On the next slide, we are looking at a lot of gold.