Casa Grande Ruins is a great stop located between Phoenix and Tucson. While it may not be worth a destination by itself, it certainly makes an interesting and informative driving break. In addition to the a short film about the area, there are excellent docent-led tours and self-directed tours available.
The ruin was first described by a European in 1694. Padre Eusebio Francisco Kino described the site in his journal and was the first to call it Casa Grande, or "the great house." Built around 1350 AD and abandoned around 1450, it is one of the largest pre-European dwellings constructed in America. The site became a national monument in 1916. More than just a single structure, Casa Grande is actually a part of a larger complex now called Compound A, which shows signs of being a multi-purpose site used for housing, commerce, and ceremonies. There are other compounds nearby, none of which are open to the public. There is also a contemporaneous structure believed to be a ball court used for games of some kind. Similar ball courts are found all over the Southwest and seem to indicate some level of cooperation by peoples across the region. The ball court is visible from a viewing platform on the site.
There is a nice picnic area, plenty of parking, including some for RVs, and the whole complex is just minutes off of highway 87 between Tucson and Phoenix.