We go on the trail of 26 once forgotten ruins you really can visit.

Mesa Verde, Colorado

Andrew Gumbel writes: "The first white man to set eyes on the extraordinary ancient cliff dwellings dug into the canyons of Mesa Verde in south-western Colorado was Richard Wetherill, a Quaker rancher. After stumbling across the perfectly preserved relics of a long-vanished native civilisation he decided to recruit his brothers and some trusted friends to explore the canyons further. The result was the establishment of one of the United States's most breathtaking national parks, an eerily evocative landscape of plunging canyons and snow-kissed peaks, where the ancient Anasazi civilisation laid down roots and enjoyed 200 years of extraordinary prosperity before vanishing almost overnight around the year 1300."