5,600 years ago, patient Stone Age laborers gouged emptiness from solid living rock, fashioning a complex three-level interior that contains astounding textural detail. Covering a total of about 5,400 square feet, with its levels extending down about 35 feet, the Hypogeum was discovered by accident in 1902 near the center of the town of Paola... For about a 1,000-year span, the Hypogeum served as a necropolis, a city of the dead that eventually housed the remains of about 7,000 people. It was one of many megalithic structures strewn across Malta, built by a complex Neolithic culture that mysteriously disappeared around...