Xochicalco

Xochicalco rose after Teotihuacán fell and held the hills of Morelos for around two and a half centuries from about 650, a planned city on terraced hilltops with walls, ditches and a controlled entrance, built by people who clearly expected trouble. Its centrepiece is the Temple of the Feathered Serpent, whose base is carved in a continuous relief of serpents coiling around seated figures, thought to record a gathering of astronomers adjusting the calendar. Cut into the hillside is an artificial cave with a hexagonal shaft to the surface, so that around the zenith passages in May and July a beam of sunlight falls to the floor. The museum on the ridge was built to run entirely on solar power.

What you actually see

• The Temple of the Feathered Serpent - continuous carved relief around the base.
• The observatory cave - a shaft that drops a sun beam at the zenith passages.
• The ballcourts and terraces - the planned defensive layout across the hills.
• The site museum - one of the first buildings in Mexico run on solar power.

When to go

November to April is dry and clear. The observatory cave is at its most striking in the weeks around the zenith passages in mid-May and late July, when visitor numbers spike and access is timed. Mornings are best, since the hilltop has no shade.

Honest expectations

The hilltop is fully exposed and the walk between groups is long, so heat and sun are the main challenge. The observatory cave has restricted access and is closed at times for conservation. It sees far fewer visitors than Teotihuacán, which is part of the appeal, but it also means fewer facilities on site.

Nearby

Cuernavaca is forty minutes; the Popocatépetl monasteries are an hour east.