Recently, amateur archaeologists have uncovered a network of underground passageways at the vast and decadent villa that the Roman emperor Hadrian built in Tivoli, Italy.
Elites, friends of the emperor and those who came on business of state would come through the main entrance and experience the opulence and beauty of the surroundings.
But below ground, Hadrian's architects built a parallel world of underground passageways.
The passageways allowed thousands of merchants, slaves and carts bearing goods to enter the villa and keep it running without causing commotion on the street.
The existence of tunnels had been known for some time from ancient plans of the grounds and many had been excavated. But over centuries, most of the tunnels had been filled in with soil. So archaeologists suspected there could be other, as-yet-undiscovered tunnels in more remote parts of the villa.
So researchers enlisted the help of a group of amateur archaeologists and speleologists with Sotterranei di Roma, or Underground Rome, to help them excavate near a remote part of the Villa known as the academy.
The team rappelled into the caverns and carried countless buckets of dirt out.
Some of the tunnels were just a few feet wide, while others were vast and spacious.
Sometimes they had to wriggle through incredibly narrow holes to keep working.
Here, Sotterranei di Roma member Marco Placidi crawls through a small hole into the tunnels.
They recently found a completely new tunnel network, leading from the Academy to the Grande Trapezio, one of the major arteries in the underground network. Though it's still a mystery what this region of the network was used for, it was leading to the more private part of the Villa where Hadrian may have gone to be alone or with a few select friends.