Cusco is a charming and pleasant city. Quechua Indians wear their colorful native dress, and the main square is one of the best places to haggle with a street vendor for an alpaca sweater. Food and drink options are varied and tasty. Corn is an important staple of the region. You can often find tamales and corn on the cob, or buy chicha, a sweet drink made of purple corn and fruit. Make sure you try the famous Peruvian Pisco Sour, a libation made from a powerful white grape brandy. You may also want to sample some coca tea. Many native Peruvians chew on the leaf of the coca plant, as they have for hundreds of years. The coca leaf produces a mild stimulant effect that is supposedly an effective treatment for low-intensity altitude sickness. Saqsayhuaman is the first important site outside of Cusco, on the way to the Sacred Valley. Forming the head of the Puma shape that outlines Cusco, it is comprised of three superimposed platforms, whose edges are zigzagged in the shape of the Puma's teeth. It was nearly impossible to attack the fortress from the ground level, as an aggressor's back was always exposed at some angle. A center field beneath the zigzag walls is the site of the yearly Inti Raymi festival, celebrating the winter solstice on June 24.