Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

Breathtaking and huge 430 year old maps of Italy.

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

Gilded heaven for philatelists and architecture freaks, still in full working order despite sitting atop tremulous ground.

Frida Kahlo's childhood home, now a museum of her life and works.

66,000 pieces of art, donated by one of the world's richest men.

Once designed as the entrance to Buckingham Palace, this structure was later relocated and stands as a victory arch.

Chelsea's soldiers were given strict orders when crossing this historic bridge.

Black cat statues guard this temple-like Egyptian revival factory.

Lovers proclaim their unbreakable bond by leaving their names on locks fastened onto the Shoreditch fence in East London.

These official units of measurement—including chains and perches—lie hidden beneath tourists' feet in a popular London hub.

Scattered throughout London are ancient remnants of the city's former bounding wall.

Originally meant to hold a statue of King William IV, this support sat empty for years. Today, it hosts a rotating cast of public artwork.

Order a salt beef-loaded beigel at any hour of the day or night at this East End institution.

Preserved behind glass, the ruins of a medieval building used to store human remains.

This pub boasts a curious history and may have inspired a Dickens character.

A beautiful little museum hidden away in the heart of Barcelona holds a treasure trove of Ancient Egyptian artifacts

This replica medieval European village in the Dominican Republic was built by a Hollywood set designer.

The current seat of the Parliament of Andalusia was once the epicenter of the Great Plague of Seville.

Spain's largest bullring offers a unique glimpse at architecture and history.

A hidden three-foot-wide house separates these two regal churches.

This restored Portuguese cafe may well be the most beautiful place in the world to grab a Big Mac.

One of the most beautiful bookstores in the world hides a neo-Gothic interior behind an art nouveau facade.

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