19. Underwater Rock Cairn
A massive stone structure was discovered under the Sea of Galilee in Israel and archaeologists were baffled as to how it got there.
Many believe that it was built on land and water levels continued to rise until the whole monument was submerged.
The structure is estimated to be almost 600,000 tons and some historians even believe that it was actually built underwater.
But the real mystery lies in why such a large structure was created at all, as it doesn’t seem to fit any of the regular descriptions we use to classify large-scale monuments in that area or time period.