This stately estate house features a tower covered in a bright, modern mural.

Hungarian self-built castle.

Castle and secret tunnel withstood a siege until its owner was killed by the Holy Roman Empire, while sitting on the toilet.

The Last Home of an Executed King.

Lebanese castle built by one man, over a lifetime.

An extraordinary mechanical calculator designed by the mathematician and philosopher Gottfried Leibniz.

An abandoned guano-mining city in the South Pacific.

A surreal museum of extraordinary industrial objects.

A valley of unique erosion patterns lends to a view like nothing on Earth.

Where the high court feasted, frolicked, and high courtesans put their royal lovers' diamonds to the test.

Mother Nature outdoes herself with this stunningly beautiful set of caves carved into marble.

Whisper secrets in a busy station only to be heard on the other side of this acoustic arch.

An antique curios dealer and hybrid taxidermist.

Peek through a transparent pyramid and drink in the mountain made of books.

Sacred waters rescued from the wrath of a volcano.

A harem-inspired Moorish fantasy design in a Victorian-era Welsh castle.

An Escher-inspired library dedicated to the wonders of the human mind, yet closed to the public.

Pompeii's less famous neighbor is still revealing her secrets.

Recently restored menagerie of Victorian-era beasts.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

A Barbary Coast watering hole built into a Gold Rush shipwreck.

The private clubhouse for the members of the Academy of Magical Arts.

The headquarters of the Mahanikai school of Buddhism, Thailand's largest monastic order.

Centuries-old bridges grown from tangled roots.