The now-abandoned tunnels were built for the transcontinental railroad on the route where the first wagon train entered California.

A small part of Russia that does not touch any other part of Russia.

These magnificent city walls rise from the barren sun-baked Spanish plains like something straight out of a fairytale.

A phenomenal assembly of pueblos in New Mexico is the most complete example of ancient ruins north of the border.

The world’s highest ski resort was deserted after an 18,000-year-old glacier melted away.

This 170-year-old Swiss guesthouse built into the side of a mountain is best accessed by a cable car.

Two nearly identical Chinese pagodas stand side by side, along with ancient stone relics.

Rainbow-hued in the summer and crystalline in the winter, this salty lake has inspired battles, temples, and plenty of awe.

The world's largest prehistoric copper mine had 30,000 animal bones scattered throughout the maze of passageways.