This hill made entirely of ancient Roman jars was simply a garbage dump to the people of the time.

An 18th-century post box used to alert the church of sick and ailing foreign pilgrims.

Plaques on its facade commemorate the Tiber's most destructive deluges.

A detailed pachyderm supports Rome's smallest Egyptian obelisk.

A master of trompe-l'oeil creates a stunning, tourist-fooling dome out of a flat ceiling.

A statue representing a lost Roman profession that was vandalized for centuries.

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

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

A sculpture serving as an homage to Pope John Paul II.

An alchemist's "magic door" stands in the middle of a Roman park.

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

The martyr's wax-enhanced skeletal remains lie preserved in a glass case in the Santa Maria della Vittoria in Rome.

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

The spot where the fascist dictator made some of his most famous speeches including declaring war on Britain and France.

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

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

The Habsburgs' royal collections of art and wonders.

Vienna's diversity-themed traffic lights were inspired by the Eurovision Song Contest.

The solemn exterior conceals an opulent interior of this 17th century church.

Apartment complexes built into huge repurposed natural gas tanks.

Vienna's giant wonder wheel had a starring role in one of the greatest noir movies of all time.

A neo-Gothic mansion now houses a wunderkammer of analog tech that hits on all the senses.

Op-art architecture designed for happiness.

A rooftop restaurant hides in plain sight atop Vienna's Palace of Justice.