The intricate stonework of Machu Picchu serves as a testament to Incan engineers.

The ghost town left by the worst nuclear disaster of all time is being taken over by nature and urban explorers.

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

On Japan's Tashirojima Island, cats are king.

This artificial cave looks like something out of a fairytale.

Ruined 11th century abbey built by King David I in Edinburgh, Scotland.

The final resting place of soldiers' loyal canine companions.

This whimsical castle of grottoes was the labor of love of a French postman, and one of the greatest achievements of outsider architecture.

This 1,300 year old monastery built atop a single rock was once only accessible depending on the whims of the tide.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

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

Rebuilt remains of a temple to Roman god Mithras.

The anatomical-pathological collection of a man who changed surgery.

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