The Wari abandoned Cerro Baúl and all their other cultural sites about AD 1000. Why they chose to leave Cerro Baúl remains a mystery, but they left ample evidence of a planned, if destructive, departure. They cleaned out functional buildings, but ritually destroyed ceremonial buildings, including the palace, temple and brewery.
Final ceremonies, such as a feast at the palace, ended with igniting the combustible parts of the structure. Later, the stone walls collapsed, covering and protecting the remains for a thousand years.
The brewery preserved the most intriguing evidence. Shawl clips found in the ruins showed that elite women were the brewers. In Inca times, Ryan Williams at the Field Museum of Natural History in Chicago, notes that noble women called "virgins of the Sun" are known to have brewed beer...
More at the New Scientist about this now-departed ancient people and their awesome 64-ouncers of beer, shown above.