Underground tunnel stairway
Giant underground water tank in Tokyo used with the to help control flooding – 177 meters (580 feet) long and 22.4 meters (73 feet) high
Bomb shelters never seem to go out of style – This article documents several people and organizations that have constructed large bomb shelters. The writer spends a night in an underground shelter and concludes that they aren’t for him. His article sheds a slightly negative view on the long term viability of shelters.
Secret bookcase passage
Underground stairway tunnel
Underground bunker vault door below the Greenbrier Hotel in West Virginia
Guard watching a bank vault door
Ft. Knox gold stash
Giant round bank vault door open.
The hidden passage bookcase that Anne Frank hid behind.