Stonehenge is a massive stone monument located on the Salisbury Plain in Wiltshire, England. It was built between 5,000 and 4,000 years ago and has evolved over 10,000 years. The site contains two types of stones - larger sarsen stones that weigh up to 25 tons each and were brought from nearby, and smaller bluestones that were transported from Wales over 140 miles away. Stonehenge and its surroundings have been designated as a UNESCO World Heritage Site since 1986 due to its archaeological and historical significance.