This ancient hydrological marvel is now the base of a modern outdoor cinema.

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

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

A sharp sculpture made of thousands of pieces of jagged glass.

A former military hospital is now used to study and preserve artifacts of the Acropolis.

Underneath one of the region's most historic roads lies the home of Plato's successor.

An ancient Greek monument and a Byzantine church coexist inside this cave.

A preserved portion of an ancient Athens barrier is displayed in a hotel basement.

The ruins of an ancient mansion sits in front of and underneath a contemporary art gallery.

When construction began on this hotel, developers were surprised to find the ruins of an ancient civilization.

The ruins of an ancient fortification wall sit in front of and underneath this boutique hotel.

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

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

View the ancient remains of buildings and the ancient "River of Hades" before hopping on a train.

According to legend, this ancient column contains healing properties.

This abandoned shopping arcade has new life as an art installation.

An ancient site that has revealed incredible artifacts including portions of the Themistoclean Wall.

There are many Byzantine-era churches still standing in Athens, but this is the only one with a 2,500-year-old column rising through its roof.

A tiny Greek Orthodox church from the Ottoman era hides on a busy city street.

This Ottoman-era Greek Orthodox Church was built to honor Agia Pareskevi, a Christian saint.

Preserved portions of Athens's ancient defenses are on display in a subterranean parking garage.

The ruins of an ancient Roman tomb hidden in the basement of a trendy clothing store.

One of the best collections of Byzantine art housed in a magnificent, 19th-century neoclassical home.

The site where hundreds of Greeks were tortured by the Nazi secret police is now a cosmetics store.