Built on the foundations of an ancient Roman villa, the unique architecture of this castle on the Catalan coast was used as a set for 'Game of Thrones.'

The 20-mile causeway that separates the Netherlands from the sea.

This former Baroque palace on the historic Calle Montcada is a rare architectural gem and was once the meeting place of an aristocratic scholarly society.

This fountain was designed to honor the man who helped bring water to Barcelona.

A hidden church in a hidden courtyard tells the story of the Miracle of Amsterdam.

In the days before house numbers, these colorful signs held clues about various buildings' purposes.

Some 80,000 Delft Blue tiles line the inside of this Amsterdam walkway.

A Dutch passageway's artistic, aquatic-themed makeover pays tribute to the capital city's famed waterways.

The world’s largest street art museum.

An ancient passage filled with stalls selling used books, once frequented by Vincent Van Gogh.

A beautifully eclectic mix of architectural styles.

The world's first zoo for microbes collecting the horrible and wonderful things living on and around us.

Preserving the research tools, unexpected inventions, and odd collections of generations of college professors.

Rejoice at Amsterdam's ‘pop temple,’ a former church reborn as a raucous music venue.

Amsterdam's former hotspot for public executions and dissections.

The Tudor-style cottage in the middle of the square is not quite what it seems.

A quartet of tiled art pieces adorn the floors of this prestigious art museum.

The oldest operational cathedral in the U.S. has one shell of a way of projecting speakers' voices.

A museum and shop on Bourbon Street located in the French Quarter.

Striking images of New Orleans history, including colonizers, soldiers, Klansmen, scientists, sharecroppers, and more, are depicted in frescoes that line the walls of this transportation hub.

An ancient burial ground believed to have been used for ritual sacrifice.

Also known as the Great Mosque of Damascus, this is one of the world's largest and oldest mosques.

One of the oldest monasteries in the world is a key pilgrimage site for both Muslims and Christians.

This handsomely carved wooden church is more than 800 years old.