Stonehenge, England

Stonehenge, constructed in multiple phases between approximately 3000 BC and 1500 BC, remains one of the most enigmatic prehistoric monuments in the world. Its largest stones, the sarsens, weigh around 25 tonnes on average and were transported from Marlborough Downs roughly 19 miles away. The monument is aligned with the summer solstice sunrise and winter solstice sunset, demonstrating sophisticated astronomical knowledge.