Nine centuries-old fortresses guard the walls of this medieval Romanian city.

This communist behemoth is the heaviest building in the world and a legacy of a brutal regime.

This massive complex is made up of hundreds of smaller temples that date back to the ninth century.

The name of this ancient Indonesian temple translates as "Elephant Cave" but it could be more accurately called "The Hellmouth."

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

The oldest inn in Kilkenny was established by the first convicted witch in Ireland.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

This curious, round temple is the oldest still-standing marble building in Rome.

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

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

Installed in an act of one-upsmanship, the annual sundial in this church is also a symbolic victory for the Gregorian calendar.

Jesus' footprints and the first catacombs in the world.

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

Architectural monsters are devouring this palace's every door and window.

2300-year-old Roman road connecting the empire.

The only "Egyptian" pyramid in Europe and the legendary tomb of Remus.

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

Rome’s legendary peephole vista is also a former Crusader stronghold.

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

Portugal's National Pantheon has a history of curses, collapses and financial problems.

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

A massive marble foot is tucked away in a small alley near the Pantheon.

A detailed pachyderm supports Rome's smallest Egyptian obelisk.

Tables of secondhand books fill the inner courtyard of this 17th-century stock exchange.