Stonehenge 
Five-thousand-year-old Stonehenge is the most famous prehistoric site in Europe, but it remains both a tantalising mystery and a hackneyed tourist experience. It consists of a ring of enormous stones topped by lintels, an inner horseshoe, an outer circle and a ditch. Although aligned to the movements of the celestial bodies, little is known about the site's purpose. What leaves most visitors gobsmacked is not the site's religious significance but the tenacity of the people who brought some of the stones all the way from South Wales. It's estimated that it would take 600 people to drag one of these 50-ton monsters more than half an inch. The downside of Stonehenge is that it's fenced off like a dog compound; there are two main roads slicing past the site; entry is via an incongruous underpass; and clashes between new age hippies and police at summer solstice have become a regular feature of the British calendar.