Ihuatzio is a Purépecha archaeological site just north of Lake Pátzcuaro, with broad platforms, ceremonial spaces, and views across the basin. It is less restored and less visited than Tzintzuntzan, but that is part of the appeal.
The site works well as a taxi excursion from Pátzcuaro, especially if you are interested in the region before the Spanish arrived. Bring water and a hat; there is little shade once you are on the open platforms.