A model train wonderland hidden beneath Gare de l'Est station.

The last remaining relic of San Francisco's glittering 1915 Panama Pacific Exposition.

An artsy hidden staircase leads to breathtaking views of San Francisco.

A huge musical instrument played by the ocean.

The industrial architecture honors the laborers who brought the Exposition Universelle of 1900 to life.

Remains of Roman amphitheater hidden in a sleepy quarter of Paris.

This triumphal arch celebrating the Sun King's conquest of Lille is a masterpiece of military architecture.

Tables of secondhand books fill the inner courtyard of this 17th-century stock exchange.

This banal Parisian entranceway is not what it seems.

The water-powered carriages are long gone, but for over a century this funicular railway has been the fastest route to the highest point in Paris.

A counter-culture bookstore like no other hides in plain sight in the streets of Paris.

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

Ghosts of France's colonial past.

In 1927, a biplane disappeared while attempting to complete the first non-stop transatlantic flight between Paris and New York City. This memorial stands at the last place it was seen.

Eighty million natural history specimens call this gargantuan museum home.

Kings Cross Station pays tribute to its role in Britain's best-selling book series.

105-foot wide giant metallic flower blooms anew every day in the heart of Buenos Aires.

A bright little alley in La Boca is a part of tango history.

Buenos Aires' city of the dead contains some very famous remains, including Eva Perón.

This historic, palatial theater is now one of the world’s most beautiful bookstores.

This abandoned church in central Lyon is missing its front stairs.

A tiled, multi-level garden of survival in Lyon.

This hidden garden boasts amazing views of Lyon.

Lyon, France is home to two remarkably preserved Roman theaters, one dating back to 15 BCE.