"Holy Wisdom" overlooks the city that became its namesake.

A striking symbol of the Bulgarian capital.

This Paris art space celebrates the creativity and ingenuity that springs from abject poverty, especially in Africa.

Abandoned railway line circling the city of Paris.

The tradition of open-air secondhand and antiquarian bookselling in Paris dates back to the Renaissance.

A museum on the history of Paris, including a set of Napoleon's toiletries, Proust's room, and relics of the Revolution.

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

Site of a classic 19th-century physics experiment to prove the earth is rotating.

This massive library holds what was once the largest book collection in the world.

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

A former Latvian headquarters of the brutal KGB secret police is now open as a grim reminder of their atrocities.

Flamboyant architecture from the turn of 20th century.

This charming Latvian lane doubled as Baker Street on the Soviet Union’s version of Sherlock Holmes.

Latvia’s first skyscraper, nicknamed ‘Stalin’s birthday cake.’

These giant yellow bowling pins seem to be defying gravity.

This centuries-old gothic monster has been converted into a sprawling, glossy bookstore.

The official motto of Luxembourg reminds passersby of the Luxembourgish commitment to their national identity and sovereignty.

Bridge that died in war and was resurected.

A former bank seized as a sniper vantage point during the Bosnian War is now a secret graffiti art gallery.

The remains of the last Bosnian fortress to fall to the Ottomans are still standing.

The haunting ruins of a military fortress turned astronomical observatory sit on a Sarajevo mountaintop.

A war-torn Olympic relic is being overtaken by graffiti and nature.

This historic timepiece is thought to be the only public clock in the world that keeps lunar time.

A monument on the pavement marks the spot where two cultures that shaped Sarajevo come together.