Houska Castle, Czech Republic
The Houska Castle in the Czech Republic was built in the 13th century to cover a bottomless pit that was supposedly an entrance to hell. Local legend has it that half-human, half-animal entities would climb out of the pit at night and descend upon the Czech countryside.
While the castle looks quite ordinary from the outside, it reportedly has no windows and no water source – its sole purpose is to cover up the pit. During World War II, the Nazis apparently used the castle as a base to utilize the pit’s evil powers! These terrifying stories have prevented people from exploring the inside of the cave as of yet.