Approaching Yagul from the main road, you can make out a large white rock painting of a person/deity/tree/sun on a cliff face on the Caballito Blanco rock outcrop to your right. This is the most obvious feature of the Unesco World Heritage site, the Prehistoric Caves of Yagul and Mitla, which stretches about 6km east from here.
Caves here have yielded evidence of the earliest plant domestication in North America, about 10,000 years ago, and other valuable details about the transition from hunting and gathering to agriculture over a period of several thousand years.
The Unesco-protected caves are difficult to visit independently. Your best bet is to hook up with Tierraventura on a day-tour to the important Guilá Naquitz cave (M$1500 per person). The trip includes a three-hour hike.