Oberto Airaudi was 28 years old when he began his great work in 1975.

Over the next 15 years, Airaudi and his New Age followers secretly dug a massive underground temple beneath his suburban house in northern Italy. Spread over 300,000 cubic feet on five levels, which are connected to one another by a complex system of corridors, the temple is sometimes called the eighth wonder of the world. Today the temple is open to the public and tourists can pay to stay the night. But the place has a dark side. Previous members have accused it of being a manipulative cult.