The Hypogeum of Sal Saflieni was not even discovered until 1902. Perhaps initially a sanctuary and ultimately a burial place of some kind, the Hypogeum is the only preserved example of subterranean labyrinth architecture in Europe. In use from 4000 to 2500 BCE, the structure has three levels that are painted with ornate designs and architecture carved out of the rock.
The most mysterious aspect of the edifice is a special chamber, known as the “Oracle Chamber,” in which words spoken at a normal volume are amplified a hundred times and audible throughout the entire structure. Whether this design feature was intentional and how it was used is unknown.