Get yourself an ice cream at
Little Man Ice Cream! It's quite the landmark building.
Denver Botanic Gardens ($15/adult) near Cheesman Park is a favorite of mine, but it would depend on your interests. Same for the many museums.
Forney Museum of Transportation is a fun gearhead museum in the city. If you want to get a mountain hike or drive in, the city of
Golden (Coors Beer HQ) is one of the easiest places to get to for that though there will be traffic. Just keep in mind that there's a HUGE outdoors culture so expect anything out in the warm sunlight to be crowded on a weekend.
Hope you and your wife have a great weekend.