5. The Fort Zverev, Russia – It was built by the engineer Constantin Zverev in the 1870s. It was the pride of the Russian army. Now it’s just a ruin with an incredible story. Used for the storage of napalm, the fort went through a terrible fire in 1970. Then, the napalm was lit, the temperature rose to 2,000 degrees, which made the material from which was built the ceiling of the fort (brick) to melt. What resulted was a kind of artificial cave with “stalactites” made of red brick.

Source & photo credits: glamgrid.com