Built around AD 1350, Casa Grande (Big House) is the country's largest existing Hohokam structure, with 11 rooms across four floors and mud walls several feet thick. It's in reasonably good shape, partly because of the metal awning that's been canopying it since 1932. Although you can't walk inside the crumbling structure, you can peer into its rooms. A few strategically placed windows and doors suggest that the structure may have served as an astronomical observatory.
Experts aren't 100% sure of the purpose of the oval ball pit, one of about 200 found regionally in Hohokam villages, but it may be linked to similar courts used for ball games by the Aztecs.
The visitor center has exhibits about the Hohokam society and Casa Grande itself, including a model of what the place may have originally looked like. Guided tours are offered hourly from late November through mid-April. Tours only run occasionally the rest of the year.
The ruins are about 70 miles northwest of Tucson. Leave I-10 at exit 211 and head north on Hwy 87 toward Coolidge and follow the signs. Don't confuse the monument with the modern town of Casa Grande, west of I-10 (be especially vigilant when using your phone for directions) .