The Great Wall of China - Various Locations, China - Height: Varies (6 to 8 meters on average) - Completion Year: Over centuries (construction began in 7th century BC) - Construction Cost: Priceless

Detail: The Great Wall of China, a UNESCO World Heritage site, stretches over 21,000 miles and is a testament to ancient engineering and defensive prowess.

Interesting Fact: Contrary to the myth, it cannot be seen from space with the naked eye.