'Hypogeum (meaning underground in Greek) of Hal-Saflieni, Malta' -Ancient Engineering
The prehistoric underground structure was discovered by accident in 1902 when some workers were digging a hole and broke through the ceiling. The creepy thing is they found about 7,000 skeletons all clustered near the entrance. The three-level underground structure is made entirely out of megalithic stones, andis estimated to have been built 3000 years B.C.
What surprised people even more was when they found out that male voices could reverberate throughout the entire complex if the person was standing in a certain spot. However the effect only worked if the speaking voice was in the 95 to 120 Hz range, so women's voices don't usually generate the same effect. Whoever built the Hypogeum actually invented sexist engineering.
