Naples is a time capsule of ancient life, with banks, bakeries and even Nero's famous stage hidden under the streets and in the caverns of Vesuvius.

An alternative world thrives in the shadows of this capital 'city of lights'. Host Eric Geller has special access to this dark underworld, where both the secrets of the living and the sins of the dead are revealed.

Budapest sits on top of an ancient secret. Follow Eric Geller as he uncovers a top secret WWII hospital and finds the source of the boiling healing water used by the Romans and the Turks in the caves beneath Budapest.

From secret prisons to escape tunnels, ancient caves to mines, Bucharest in Romania is ripe with folklore. Discover the history of its secret underworld.

From hidden tunnels beneath Boston to the incredible waterworld under Philadelphia, the Freemasons left behind the blueprints to America's rise.

Host Eric Geller travels through the dark and damp recesses of Berlin's secret bunkers. Engineered by the Nazis during WWII, their dark past is revealed.

From Roman baths, secret crypts, lost rivers and even Winston Churchill's hidden war rooms, London's underground world has a plethora of stories to tell.

What's at the heart of the Big Apple? Explore a tangle of engineering, history and secrets that make up a dark urban underworld labyrinth. It's the city that never sleeps!

Host Eric Geller discovers what life was like during Emperor Nero's tyrannical reign and Augustus's reforms by peeling back the hidden history of Rome.

Beneath the modern city streets, ancient underground neighbourhoods and sewerage systems reveal the technological marvels that helped advance an empire.

From plague victims being buried alive to body snatchers, illegal distilleries and castle dungeons, Edinburgh's underground world has a myriad of stories to tell.

The castles and dungeons of the Hittites are hidden beneath the sandy lunar landscape of Cappadocia. Why did this ancient empire fall?

Slave tunnels, gambling dens and opium runners: welcome to the dark, 100 year-old underworld history of Portland, Oregon, famous for being a city full of vice.