Its interior is adorned with some of the best examples of early Christian mosaics.

Ancient ruins hidden underneath a modern luxury hotel.

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

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

This holy site either displays a centuries-old cross or a complete fake.

A forgotten "city of water" underneath the famous Trevi district.

The final resting place of the poets Shelley and Keats.

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

Walk through spectacular aisles of hanging meat and wagon wheel–sized cheese at the world's largest wholesale food market.

Paris' linguistic guide to the international language of, yes, love.

The oldest stone house in Paris was built by its most famous alchemist.

One of the most beautiful bookstores in the world hides a neo-Gothic interior behind an art nouveau facade.

Ancient catacombs form the foundation for this Rococo orgy of a church.

This historic streetcar system has been running since the 19th-century.

This museum is home to one of the biggest collections of printing press technology—plus a river view.

The history of drinking is told through 1,800 cups, chalices, and glasses at this exhibit.

One of the smallest bookstores on the planet.

Located in the thermoelectric factory that once powered the entire city, this Portuguese museum is shockingly fascinating.

This tile-work piece featuring a chicken riding in carriage is both a remarkable artistic creation and a social commentary of politics and culture in 17th-century Portugal.

Tucked away inside this concrete building is a church and its grand display of brutalist architecture.

This once-forgotten oasis in the middle of Lisbon was first created over a century ago quite by accident.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

Centuries before the modern seismograph, Armenian monks measured quakes with this tilting pillar.

This house's itty bitty size means no humans allowed.