The Vatican's secret porn-festooned bathroom was painted in erotic murals by one of the greatest artists of the Renaissance.

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

Remnants of a 4th-century church with vivid medieval frescoes and ancient sarcophagi hide beneath this old basilica.

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

A forgotten "city of water" underneath the famous Trevi district.

A Baroque mansion with ties to legendary magicians and alchemists.

A steampunk-styled three-floor factory churning out art, activism, and electronic beats.

Walk through Czech history in Prague's largest graveyard.

This extinct volcano rises above Edinburgh and is special for its panoramic views over the city.

Overlooking the burial ground is a tower designed to prevent thieves from snatching the recently deceased.

Enter this small nook and you'll be surrounded by 360 degrees of street art.

This alley off Edinburgh's Royal Mile contains remnants of the city's seedier history.

These steps offer a breathtaking view of one of Europe's most besieged fortresses.

One of Edinburgh's oldest pubs hides a 19th-century skittles alley in the back.

Now home to a drinking establishment, this building has a macabre history.

Anonymously sculpted and donated, these sculptures made from poetry books and pages are sprinkled around the city.

Sprawled across the Great Hall ceiling are various constellations and images relating to the zodiac.

A verdant 17th-century-style garden hidden along Edinburgh’s Royal Mile.

Long abandoned underground complex to keep royals safe from a nuclear war that never came.

This obscure walkway links Edinburgh’s Old Town with one of the city's prime vantage points.

There are plenty of wonderful panoramic vistas in Edinburgh, but not many are hidden smack in the middle of the Old Town.

Near the former site of numerous witch burnings, this lavish Edinburgh mainstay pays homage to Scotland's brutal history.

Tiny effigies of the victims of Edinburgh's famous Anatomy Murders.

This Little Rock legend has survived decades of rowdy crowds, three fires, and a zombie wedding.