About 12 miles northeast of Farmington in the town of Aztec, this UNESCO World Heritage Site preserves a large Ancestral Puebloan complex built between 1100 and 1300 CE. The ruins include multi-storey masonry structures, ceremonial rooms, and — the highlight — the Great Kiva, the oldest and largest reconstructed great kiva in North America. You can walk down into it and stand in a circular room 48 feet in diameter, with massive wooden columns supporting a reconstructed roof.
The site is compact and well-interpreted. The self-guided trail takes about an hour; the visitor centre has good exhibits on Ancestral Puebloan culture and the archaeology of the San Juan Basin. Come early in summer — it gets hot by mid-morning and there's little shade on the trail.