Chankillo is a large ceremonial center covering several square kilometers in the costal Peruvian desert. It was better known in the past for a heavily fortified hilltop structure with massive walls, restricted gates, and parapets. For many years, there has been a controversy as to whether this part of Chankillo was a fort or a ceremonial center. But the purpose of a 300meter long line of Thirteen Towers lying along a small hill nearby had remained a mystery..
The new evidence now identifies it as a solar observatory. When viewed from two specially constructed observing points, the thirteen towers are strikingly visible on the horizon, resembling large prehistoric teeth. Around the observing points are spaces where artifacts indicate that ritual gatherings were held.
The current report offers strong evidence for an additional use of the site at Chankillo � as a solar observatory. It is remarkable as the earliest known complete solar observatory in the Americas that defines all the major aspects of the solar year.
The photos at that link give a good indication at how it was used.
More here, too.