The Huaca de la Luna is a massive Moche ceremonial pyramid built in stages between roughly 100 and 800 AD, about 8 kilometres south of Trujillo. Its outer shell conceals an inner pyramid, and that one conceals another — each successive Moche ruler built a new layer over the existing structure. The result, now partly excavated and open, reveals a sequence of polychrome murals that are among the most spectacular pre-Columbian paintings in South America.
The guided tour (included in the entrance fee) walks you through the excavated sections, explaining what the murals depict and how archaeologists have interpreted the ritual ceremonies performed here. The adjacent Huaca del Sol, the larger of the two mounds, is still under excavation and not open to visitors, but you can see it from the site.
The site museum near the entrance is worth a visit before you climb — it gives context that makes the murals make sense.