What were the Aztec people doing here, so far north of Mexico?

Nothing! It was not the Aztecs that built the settlement at this location, but rather the Pueblo people. The Spanish had a habit of simply calling everything "Aztec" and they so named the ruins on encountering them.

Built over a 30-year period in the late 10th century, this site was occupied for over 200 years. Then suddenly, the inhabitants simply left. No one is sure why but by the year 1300, they were gone.

The National Monument offers a walking tour around and through the remains of the community. Rooms are small and doorways low, but the site gives one a good idea of how life was.