A solar-powered primary school inspires hope and experimentation in a country ripe for energy innovation.

This 3,800-year-old site contains markers used to study the movement of the sun and moon and create a lunar calendar.

Stone pillars and a petrified wedding party in the hills of North Macedonia.

Space-age monument to an early 20th-century uprising.

This off-beat, quirky communism-themed bar isn't afraid to poke fun at its history.

The elliptical citadel resisted the advance of the mighty Ottomans several times, thanks to the military prowess of the "Dragon of Albania."

Hundreds of thousands of concrete bunkers crowd Albania long after the fall of Communism.

Hidden in a grotto 26 feet below Nottingham's oldest hotel, this stylish subterranean drinking den is notoriously hard to find.

An engineering error ensured this cavernous 350-foot-long subterranean thoroughfare was never used as intended.

Rome's semi-secret peephole vista is also a former Crusader stronghold.

The largest of Denmark's seven mysterious round churches stands on an island in the Baltic Sea.

This mosaic-lined medieval church was built by the world's first admiral and still holds mass in ancient Greek.

Rare remnants of the brick-domed ovens birthed in the Durham coalfield during the Industrial Revolution.

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

This floating garden in the sky is straight out of a fairy tale, but the real thing is nothing short of magical.

Early Medieval stones sit on display at the beautiful Govan Old Church in Glasgow.

One of the largest barracks of the Austro-Hungarian monarchy's military is now an abandoned ruin.

Spend the night in this formerly abandoned traditional Scottish village.

The Mexican painter Diego Rivera created this unusual museum to display his collection of pre-Hispanic artifacts.

Strange rock formations tower above the river that snakes through this enchanting Icelandic canyon.

The shape of this old salt factory complex was inspired by the course of the Sun.

An abandoned socialist utopia built in the late 19th century.

The name of this ancient Indonesian temple translates as "Elephant Cave" but it could be more accurately called "The Hellmouth."

An extraordinary "City of Caves" carved from solid stone.