The largest of Denmark's seven mysterious round churches stands on an island in the Baltic Sea.

This remote island, home to the easternmost point in Denmark, once hosted pirates and a military fortress.

These barriers stand as stark reminders of Northern Ireland's troubled past.

This massive monument has been telling the time for 150 years—at a slight angle.

Belfast's namesake river still winds below the city center, hidden from sight.

These engineering masterpieces are a dominant feature of the Belfast skyline.

The ship built to ferry passengers and goods to the doomed Titanic is now the last remaining White Star Line vessel.

A museum marks and documents the site of the Titanic's launch.

A stunning Victorian abbey and walled garden on a lakefront.

Despite the name, this 16th-century structure in Galway wasn't built by the Spanish.

Believed to be the former location of one of the earliest Viking assemblies in Europe.

World's largest working waterwheel has been around for over 150 years.

A hidden three-foot-wide house separates these two regal churches.

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

This giant sculpture made of trash is a critique of society's wastefulness.

This enormous censer uses a pulley system installed over 400 years ago.

The oldest Roman lighthouse still in use.

Natural stone arches form a walkable "cathedral" at low tide, then disappear entirely when the water returns.

A statue honoring the tragic heroine of a Spanish literary masterpiece.

A street where pouring cider is an art form.

Two large posteriors in one giant statue.

The much-loved protagonist of famed Argentinian comics can be found sitting on a park bench.

The surviving remnants of a destroyed medieval church now stand in a public park.

The atmospheric ruins of a historic church can be found on a hill above the city of Oviedo.