The narrowest street in Paris.

A lone cannonball remains lodged in the walls of the Hotel de Sens as a sober reminder of a revolution.

This banal Parisian entranceway is not what it seems.

The curious underground history of keeping Paris clean.

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.

An overlooked marble is the only surviving in-place 18th century example of the measurement that changed how we define distance.

Exquisite wall sculptures carved in secret by an early quarryman in an obscure corner of the Paris Catacombs.

Known as the "Dodo Manège," this carousel features a herd of animals that have disappeared—or may be gone soon.

The history of radiation is on safe display at the foot of a radiation science laboratory.

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

A surrealist timepiece by the artist of melting clocks.

High atop the Eiffel Tower is a small apartment built exclusively to entertain the science elite and make the rest of Paris jealous.

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

Notorious artist squat renovated into legal studios.

Poet William Blake penned some of his most famous work during his brief stay at this beloved country cottage.

Rare wooden escalators lead deep down into an otherwise staggeringly monotonous tiled tunnel.

The once-a-day siren is a reminder of the days before time was standardized.

The largest timber structure in Europe.

One of these two land speed record-breaking vehicles went so fast it shattered the sound barrier.

A discarded movie prop that was the original monolith for "2001: A Space Odyssey."

The largest preserved walking dragline excavator in Western Europe.

This historic club for wayward boys has shaped some of the biggest names in music almost as much as they have shaped it.

Cycle the solar system—from the sun to Pluto—right here on earth.

The "beautiful" equation predicting the movement of all electromagnetic particles is engraved in front of Newton's tomb.