This 11th-century castle sits so low you can't see it behind the surrounding buildings.

Science meets wall art to highlight the beauty of famous mathematical equations.

The works of poetry's biggest names grace the walls of the city of Leiden, all carefully painted by hand.

Lumps of significant stone from around the world surround a flaming monument for peace.

An ancient passage filled with stalls selling used books, once frequented by Vincent Van Gogh.

Amsterdam's former hotspot for public executions and dissections.

A beautifully eclectic mix of architectural styles.

An Amsterdam street lined with antique shops each one dedicated to a different obscure collection.

Three connected pink triangles memorialize persecuted gays and lesbians throughout history.

The attic of a four-century-old canal house hides a clandestine church.

This unique religious structure is an architectural gem with arresting ocean views.

Yale University's home for rare works, including the mysterious Voynich Manuscript.

While many places make the claim, the Library of Congress says this restaurant is the birthplace of the hamburger.

The headquarters of the famous Yale society.

The little-known, 300-year history of the area includes former lives as a bustling tobacco port, parking lot, and industrial dump.

London's only public statue of the much-married monarch adorns the gate to St Bartholomew’s Hospital.

A mysterious pair of mice eating a piece of cheese is London's smallest public sculpture.

Six ravens are kept captive (but well-fed) at the Tower of London to prevent the fall of the Crown.

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the first ‘Harry Potter’ film.

One of the few remaining casualties of the London Blitz, this destroyed church has become an enchanting public garden.

A plaque hangs near the execution place of the Scottish Independence leader famously depicted in "Braveheart."

A portly statue of a golden boy commemorates an unusual cause of the Great Fire of London: the sin of gluttony.

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

A cluttered and astounding collection of antiquities and curiosities.