This small, ancient Roman temple was once a church dedicated to the patron saint of penitents.

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

In the early Roman Empire, people deemed traitors and criminals were tossed to their deaths from this rock.

This large, circular tomb is the final resting place of the first emperor of Rome.

The "Greatest Sewer" of ancient Rome is one of the oldest sewer systems in the world, and is still in use.

The engineering wonder and pleasure dome of a much-maligned emperor still holds undiscovered secrets.

The yawning maw of this pagan visage is said to bite off the hands of liars.

The massive white mound and accompanying water terraces are a striking geological oddity.

Hungarian mummies in beautiful painted coffins.

The mummified right fist of a 1,000-year-old saint-king sits inside an ornate golden reliquary.

This hidden art nouveau gem was designed by an architect in search of a national style.

From Austrians to Nazis to Soviets, this historic Budapest fortress has a history as complex as the city itself.

Built in 1870 at the bridge that connected Buda and Pest, this spectacular incline railway was almost lost forever during World War II.

This Hungarian castle was built out of cardboard and wood until it proved so popular that it got upgraded to stone.

These caves secretly held national treasures during World War II.

Only open for two days a year, this church links ancient Greek and modern Christian celebrations.

According to legend, this cavern holds the passage that Persephone used to travel to and from the underworld.

This open air archeological site houses almost as much wildlife as it does classical religious artifacts.

An abandoned Byzantine fortress and notorious prison.

Temple complex that once housed the famous statue of Nike.

Legend says this sacred tree was a gift from goddess Athena.

Swarms of dainty flying insects swarm into the Petaloudes Valley to get busy.

Large collection from the 3rd millennium BCE.

Heralded as the world's first theater, these ruins are often overlooked as they reside in the shadows of the Acropolis.