The Cave Creature

1922. Geologists explore a cave system under the ancient ruins of Babylon (Kingdom of Iraq) finding a massive stone structure. It appears to have been worshiped in some way by the ancient Mesopotamians.
Carvings in the cave wall associate it with Humbaba, a mythological demon.

The carvings tell the story of the stone giant waking up after something they did angered it. It appears to be some sort of warning, perhaps a metaphor of the decaying Babylonian empire in the XVI century BC. (Pictured: the ruins of Babylon)

Near the city, the group of geologists documented finding very large indentations in the ground. Convinced that the creature was real and these were its footsteps, they never released the location of the cave structure. It has not been found again to this day.