This North African stone complex is considered to be the oldest astronomical observatory on Earth.

A labyrinth hides in plain sight at each of the city's 270 Tube stations.

This centuries-old Italian chapel hangs midway down a sheer cliffside.

This cliff-face port is considered a masterpiece of mining engineering.

A dead saint, a deadly poison, and a mysterious holy ooze.

An immense cave that has served as an outlaw's treasure trove, an underground dance hall, a nuclear fallout shelter, and much more.

Known as the Royal Palace of the Euganean Hills, this often overlooked castle has been home for multiple noble families over the centuries.

Established hundreds of years ago, Gandan remains the premier Buddhist monastery in Ulaanbaatar.

Building owners can take out tiles for free at this repository for historic building materials.

One of the most beautiful bookstores in the world hides a neo-Gothic interior behind an art nouveau facade.

A hidden three-foot-wide house separates these two regal churches.

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