Northern Ireland's Brobdingnagian stepping stones.

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

Catacombs turned marketplace.

These engineering masterpieces are a dominant feature of the Belfast skyline.

A museum marks and documents the site of the Titanic's launch.

Tucked away in the Tower of London is the weapon once used to execute high-profile prisoners.

Famously misunderstood wonder of the ancient world

Commonly acknowledged as the only public monument to the Devil himself.

Spanish architects used seized Muslim gravestones to rebuild parts of the fortress.

A curious carving hides on a marble column in the Mosque-Cathedral of Córdoba.

A 16th-century Andalusian palace.

Over two centuries old and counting, Madrid's massive botanical garden contains one of Europe's only desert environments.

Madrid's romantically ornate crystal palace has been offering shelter to plants and art for over a century.

After the parade, students throw their beads on the tree hoping for good luck on exams.

This float factory takes the mask off of Mardi Gras and lets visitors see where the magic happens.

The celebrated eyesore created by starry-eyed sweethearts.

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

These official units of measurement—including chains and perches—lie hidden beneath tourists' feet in a popular London hub.

Richard III supposedly disposed of his nephews' bodies here in an effort to seal his claim to the throne.

The medieval woodcut-style artwork chronicles life in medieval London.

These wire animal sculptures commemorate the exotic inhabitants that once called the Tower of London home.

An architectural oddity hides in plain sight on this iconic London bridge.

The ritual has been performed uninterrupted for nearly 700 years.

Once a train station along the Great Eastern Railway this vibrant coffee shop and bar is where members of London’s creative class mingle.