The final resting place of the poets Shelley and Keats.

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

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

The former Nazi Germany concentration camp stands as a museum to remember this dark chapter in European history.

An underground city of salt.

A living art gallery painted on a canvas of Monterey pine trees.

Hundreds of stone stairs and a winding medieval bridge connect this haunting Spanish island to the mainland.

Giant topiary dog once played a role in a terrorist bomb plot.

Dublin's "Dead Zoo" serves as a window to Victorian museum design.

One of Ireland's most infamous prisons for rebels including men, women and children.

A museum that cashes in on its infamous little people while teaching you a thing or two about the Irish fey.

Amsterdam's narrowest house facade is a monument to 17th-century tax evasion.

This cheese shop also houses a museum devoted to Dutch dairy.

A curious collection dedicated to human and animal anatomy and pathology.

Established in 1638 to battle the Black Death, this botanical garden is a treasure trove of rare flora.

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

A lush indoor jungle fills this bustling Madrid transportation hub.

This stone harbor was key to Carnlough's limestone industry.

Amazing vistas await visitors to this stretch of coastline.

A unique art installation located on what was once considered the widest railway bridge in the world.

Glasgow's memorial to the International Brigade volunteers from Great Britain who fought and died in the Spanish Civil War.

This stately monument has been wearing a traffic cone hat for decades much to the delight of the locals.

A scattered trail of street art adds a pop of color to the city's stark structures.

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