Tucson has TWO National Parks that are named for and feature saguaros, or maybe two locations of the one park - Tucson Mountain District and Rincon Mountain District. Rincon MD in the far East is a little more beauty, Tucson MD in the West is ten miles from I-10.
Old Tucson is a surprising amount of fun and education.
The Desert Museum is great, but go in the morning for the best wildlife viewing. Don't confuse it with the International Wildlife Museum a few miles away. The latter is worth visiting, but features stuffed animals.
BTW, you don't have to visit the parks to see saguaros - they are all over Tucson. We have 40-something in our yard.
Matt B