For a quick break from the heat (may not be an issue if you're only there 3 days) is to drive up Mt. Lemmon. During part of the year there's snow-- not sure about July. Mt. Lemmon is within the city limits.
The Botanical gardens are very nice and display a variety of Southwestern plants and other plants from around the globe with comparable weather (think Africa, I think Australia, South America). The Botanical gardens are also within the city limits.
For dinner, check out the Pinnacle Peak Steakhouse-- it's an old west recreated town with different gift shops, a few free shows, and pretty good food at the steakhouse. Check it out at
http://www.pinnaclepeaktucson.com/ .