Mile-long cave system near Great Smoky Mountains.

This replica of the Greek structure is in the heart of Nashville.

Better known as the "Body Farm," this unique research facility has been studying how human bodies break down since the 1980s.

For two weeks every June, fireflies in the Smoky Mountains perform an astonishing light show.

This wooden recreation of a 9th century lake village looks as though it was built yesterday (which it relatively was).

A black cat protests the City Guild in Riga's Old Town.

3,000 market stands in five former Zeppelin hangars.

This bridge was constructed from the rubble of the infamous Bastille.

This statue was given to France by the United States to commemorate the centennial of the French Revolution.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

The celebrated eyesore created by starry-eyed sweethearts.

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

A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.

Museum dedicated to literary greats of the Romantic Period is also the home in which Keats met his untimely end.

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

2300-year-old Roman road connecting the empire.

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

Hundreds of lucky felines haunt the ruins where Caesar was murdered.

A fountain standing as a testament to a doomed alliance.

This former Imperial summer home was the venue for a royal slap that once echoed 'round the world.

Carvings in Turkey's Marble Road may have directed ancient Romans to a hidden brothel.

Ancient serpentine sacrifice holder that has stood the test of time.

Seven early Christians were sealed into a cave where legend has it they slept unharmed for centuries.

Five sultans and their families rest in eternal splendor, teeming with overlooked beauty and drama.