Catacombs turned marketplace.

A special shop catering to the needs of things that go bump in the night, and also helps kids become writers.

Rebuilt remains of a temple to Roman god Mithras.

Several plaster noses are hidden in plain sight around London's Soho neighborhood.

This 1920s Dutch barge is now a floating bookstore.

A subterranean ice warehouse that has lain hidden beneath central London for over a century is now open to the public.

A tongue-in-cheek arcade where the games are based on everyday life.

Winding paths and ramshackle mausoleums in the oldest "park cemetery" in London.

Banksy gives themself artistic license with this piece of London street art.

The popularity of Sherlock Holmes led to the creation of his fictional address, turning the orderly London street numbers askew.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

A charming 17th-century alley is lined with secondhand bookstores and antiquarian shops.

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

A kaleidoscopic warehouse-maze of handmade neon signs.

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the Harry Potter films.

An easily overlooked stretch of ornate window fronts and gaslight lamps that could be right from the pages of Dickens.

The ruins of a Duke's bucolic dream, where camels once roamed alongside "Dutch" windmills and faux-Italian vineyards.

A haunting collection of the vanished and disappearing natural world.

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

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

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

A horde of stray cats rule in this secluded Parisian cemetery under a bridge.

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

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