Go inside to really appreciate this 500-year-old technological masterpiece.

This one-of-a-kind Roman arch is not actually dedicated to the god Janus.

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

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

Inside this McDonald's you can dine on your Big Mac and fries next to a 2,500-year-old Roman wall.

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

2300-year-old Roman road connecting the empire.

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

A detailed pachyderm supports Rome's smallest Egyptian obelisk.

A modern, secular take on a traditional Virgin Mary motif.

Swedish skyscraper with a 90° twist.

This chimerical bridge/tunnel appears to dead end right into the sea.

Nordic giants resurrected from the sea and restored to their former greatness.

Climb to the top of its spiral spire for spectacular views of Copenhagen.

The old observatory in Copenhagen has a spiral corridor used as a racetrack.

Opulence and fantasy collide in this royal chair which is supposedly made with unicorn horns.

The de facto symbol of Copenhagen is this bronze fairytale which cannot seem to keep its head for very long.

This historic structure has been used as a mosque, a barracks, a prison, a school, and a bakery.

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

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

The Cycladic architecture makes this Athens neighborhood feel like an island paradise hidden in the shadow of the Acropolis.

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

An ancient octagonal weather station named for the eight Greek gods of wind.

A 2,000-year-old computer demonstrates remarkable engineering and astronomical precision.