This narrow Ghent alleyway is an officially sanctioned street art tunnel.

Barça football fans might see the insignia hidden in a church window as a divine sign.

Possibly the oldest church in Barcelona, this basilica has its pagan and Christian mythologies all mixed up.

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

The 2,000-year-old Roman columns are hidden within Barcelona's Gothic Quarter.

The oldest operating Mississippi River–style steamboat still navigates the Ohio River.

This hidden jockey “walk of fame” celebrates the winning riders of the Kentucky Derby.

Amsterdam's narrowest house facade is a monument to 17th-century tax evasion.

A floating cat sanctuary on an Amsterdam canal.

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

Remnants of a 4th-century church with vivid medieval frescoes and ancient sarcophagi hide beneath this old basilica.

"We Seceded Where Others Failed."

A monument celebrating the idea of reaching inaccessible places.

Meet manatees face-to-face at this zoo for native species.

The very first subway station in New York City is beautiful, decked out in chandeliers, and ... abandoned?

This bridge was constructed from the rubble of the infamous Bastille.

A 16th-century fountain marks the site of a lost medieval cemetery once filled with mass graves.

This modest marker near Notre Dame identifies the very center of Paris.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

A series of abstract, silly sculptures represent the works of a great modern classical composer.

This life-size replica of the Statue of Liberty's flame is also a tribute to Princess Diana by default.

This charming cobbled backstreet is the most Instagramable street in Paris, much to the residents' annoyance.

The first green space constructed on an elevated viaduct.

135 bronze medallions mark a French meridian line which once rivaled the hotshot Greenwich timeline.