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

Statue of death tucked in the University of Medicine courtyard.

This statue was given to France by the United States to commemorate the centennial of the French Revolution.

A scandalous Art Nouveau collaboration that set Paris all atwitter at the turn of the century.

Abandoned railway line circling the city of Paris.

Down a cobblestone alleyway is a museum dedicated to Romanticism, with a secret garden.

Behind the pink curtain, Au Bonheur du Jour, an art gallery of erotic archives.

A surrealist timepiece by the artist of melting clocks.

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

A museum of carnival attractions where you are invited to ride the rides.

The oldest stone house in Paris was built by its most famous alchemist.

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

France's most famous cemetery, with some of its most curious tombs.

The pockmarks across the building's facade are remnants of the Blitz.

The rose garden in Regent's Park where Pongo and Perdita met for the first time in Disney's "101 Dalmatians."

This churchyard arbor is surrounded by hundreds of gravestones placed there by author Thomas Hardy.

An unusual round church in London with a Templar past.

A 300-year-old tea shop that brought tea to the English people, not to mention the Queen herself.

The quaint little store that is said to have inspired a famous Dickens novel was only given its name after the book was released.

Victorian-era Londoners really wanted to believe this 17th-century cistern was actually an ancient artifact.

A network of concealed passageways lies within a busy London Underground station.

According to legend, this tomb holds the secrets to time travel.

The bar where "The Great Train Robbery" was planned was once a nexus of high society and low morals.

The Metropolitan Police refurbished the blue box (perhaps not coincidentally) the same year "Doctor Who" returned to TV screens.