An easily overlooked stretch of ornate window fronts and gaslight lamps that could be right from the pages of Dickens.

This ancient Roman arch misled treasure hunters for centuries.

An 18th century fountain and two columns are all that remains of Rome's forgotten river harbor.

The ruins of the largest gladiatorial school in Rome are largely hidden under modern streets.

In Rome’s Jewish ghetto, a 200-year-old bakery still makes the neighborhood’s historic sweets.

A magnificent waterfall is also home to the remains of a Roman hydraulic engineering system.

The best preserved Paleochristian basilica in Rome hides a number of oddities and secrets.

A treasure trove of Renaissance-era funerary art in a Roman church built on top of Nero's grave.

This beautiful park on the outskirts of Rome protects the ruins of two colossal ancient aqueducts.

Rome's semi-secret peephole vista is also a former Crusader stronghold.

Poland's oldest salt mine has nearly everything one needs to live underground forever.

An underground city of salt.

The former Nazi concentration camp stands as a museum to remember this dark chapter in European history.

An abandoned Nazi explosives plant founded by the inventor of dynamite is now an underground museum.

The final resting place of more than 200,000 people, this is one of the largest cemeteries in Europe.

A 18th century graveyard and its astonishing cortege of macabre iconography.

This tablet indicates where the tragic monarch returned to begin her tumultuous downfall.

A beautiful Greco-Roman structure houses a well once believed to have healing powers.

Inside this cathedral is a shoulder bone belonging to the Patron Saint of Scotland.

A book bound in the skin of an infamous criminal, along with countless other specimens.

Overlooked by many, the two famous Scottish warriors guard the main gate of Edinburgh Castle.

The fountain marks the area where hundreds of accused witches were burned at the stake.

17th century streets hidden under Edinburgh were once a breeding ground for the black death.

A sobering scientific reminder of the human damage caused by the advent of the nuclear age.