About 4km (2 1/2 miles) southwest of Nasca are very well-preserved stone aqueducts, part of a sophisticated subterranean system constructed by the Nasca to irrigate the fields in the pampas. There are 35 beautifully built Inca or pre-Inca aqueducts, or puquios, with surface air vents that form spirals descending to the water current. The canals, many S-shaped to slow the flow of water, still function and are used by local farmers. Nearby, Los Paredones, the ruins of an Inca trade center, is in poor shape, requiring a fertile imagination to conjure the activity that once reigned here.