This (occupied) house is 10 feet wide and full of spite.

An ingenious solution to a tricky engineering problem, this spiraling bridge takes drivers for a dizzying spin.

The old observatory in Copenhagen has a spiral corridor used as a racetrack.

This enormous spiral sculpture looks strangely out of place on the edge of a housing development.

An architectural oddity of six stories, accessed by graceful ramps.

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

A master of trompe-l'oeil creates a stunning, tourist-fooling dome out of a flat ceiling.

More than 450 years ago, an Italian nun became the first woman to paint the iconic subject.

A different Edgar Allan Poe built this charming Victorian home.

Pilgrimage site for star-crossed lovers.

One of Catholicism's four major basilicas has a series of papal portraits that are said to predict the end of the world.

Museum dedicated to literary greats of the Romantic Period is also the home in which Keats met his untimely end.

This ancient Roman prison is decorated with an upside-down cross not as blasphemy but as saintly tribute.

This beautiful park on the outskirts of Rome protects the ruins of two colossal ancient aqueducts.

The final resting place of the poets Shelley and Keats.

2300-year-old Roman road connecting the empire.

In Rome’s Jewish ghetto, a 200-year-old bakery still makes the neighborhood’s historic sweets.

The hallucinogenic center of the ancient world.

This London pub hides a peculiar secret: a recreation of the rooms shared at 221b Baker Street by Sherlock Holmes and Dr. Watson.

The first American department store, and home to the largest operating musical instrument in the world.

Only a few pieces remain of the structure that carried people and goods across the Thames for some 600 years.

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

The 19th-century pharmacy (now a used bookstore) was featured in James Joyce’s "Ulysses," and has changed very little to this day.

Leaning shelves and books galore, this location is a book lover's utopia.