Ancient paintings known as the "Sistine Chapel of Cave Art."

A cave's rare beauty held a cavernous secret hidden underground.

The world's longest known cave system.

The original home of the Lego has a huge amusement park dedicated to the iconic plastic toy.

A serpentine highway twists and turns over the treacherous Norwegian Sea.

This single room has survived the centuries with almost no deterioration.

The central mosque of this Mali town is entirely built from mud.

The Avenue of Mausolea is a series of grand palatial tombs.

The once highest point in China blends symbolic design with a kick of adrenaline.

Buildings that dynamite couldn't bring down were abandoned because of bathroom issues.

The world's first ice hotel is still one of the most elaborate and beautiful.

This Connecticut chapel is a starkly modern, and surprisingly colorful, architectural rebel.

The glowing blue Nymphaeum of Emperor Tiberius.

The fifth-longest suspension bridge the world, connecting one Michigan peninsula to another.

This chimerical bridge/tunnel appears to dead end right into the sea.

An unrealized dream to wirelessly electrify the entire Earth.

An opal mining town in the middle of Australia where people live, worship, and shop underground.

The end of the 4 Line is also the end of the line for 300,000 souls in one of NYC's most illustrious cemeteries.

One of the oldest log cabins in America is one of the last of its kind this historic Swedish dwelling remains a piece of living history.

Eccentric concrete mansion and museum designed and built by hand from the inside out.

The former home of Samuel Clemens and family remembers the happiest period of the author's life.