An ancient Roman temple first dedicated to an emperor's wife is now a church.

One of several skulls claiming to belong to the beheaded St. John the Baptist is on display at this Roman church.

This hidden Art Nouveau courtyard is an opulent feast for the eyes.

This ancient market is often referred to as the oldest shopping mall in the world.

This former Roman Catholic Church still contains the embalmed hearts and organs of 22 popes.

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

An alchemist's "magic door" stands in the middle of a Roman park.

This Roman arch marks the location of an ancient gate at one of the Seven Hills of Rome.

Its interior is adorned with some of the best examples of early Christian mosaics.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

A monumental fountain in Rome features a large statue of Moses that has been criticized for centuries.

Ancient ruins hidden underneath a modern luxury hotel.

These artifacts were discovered during the construction of the airport, with some dating back to the Neolithic period.

The heads and relics of 179 monks slaughtered by pirates are on display within this Ceonobic Monastery.

The oldest cemetery of modern-day Athens blends the modern and ancient worlds.

The oldest standing Byzantine church in Athens is tucked within a monastery in the middle of an upscale shopping district.

The only ancient site that remains on the south bank of the sacred Ilissos river.

An often overlooked ancient site in downtown Athens with substantial history (and nature).

A sprawling collection of books and manuscripts about ancient Greece that would have put their famed libraries to shame.

According to legend, this ancient column contains healing properties.

This mystical orb covered in strange symbols is thought to have been used in ancient Greek magical rituals.

Large collection from the 3rd millennium BCE.

A Byzantine-era church hidden in a wooded area below the Acropolis.

This small chapel holds the mummified heart of one of the heroes of the Greek Revolution.