In 1853, Ferdinand II of Bourbon built an underground tunnel network in Naples, Italy, in case there was a revolution and he needed to move troops quickly and secretly.
In the 1930s the tunnels were used for storing impounded vehicles. In the war, they were used as air raid shelters.... then they were abandoned, closed up and forgotten! Still full of cars and war remnants.
Five years ago they were remembered by a war survivor and reopened and are now a museum.
I find it hard to believe this stuff could have lain forgotten for so long. I find the images haunting.
This is the BBC article that brought it to my attention, but there are many articles out there.