Phoenix Art Museum is one of our favorite places to visit. It's more than just art. It makes for a great date night, as it features a cafe, and Phoenix Theater is just next door if you wanted to make a day of it. (It was one of our first dates!)
The lake is a shining star for both of us. If you're inclined to get outside and not go far, there are boat and paddleboard rentals if you're so inclined. It's also a great place for an evening stroll with Mill Avenue and the Tempe Center for the Arts on the south side of the Lake with shops and restaurants.
If you are making a vacation of the trip and heading north to Sedona, Jerome, or the Grand Canyon is on your agenda, make a stop by Rock Springs for pie. Get there early because by afternoon there won't be much (if any) to choose from. It's become a great little spot to get out and stretch your legs with shops, a stream, the cafe, and bar.