Suggestions for a short trip to Denver?

I have a business trip to Denver in a few weeks, but I'm planning on staying a couple extra nights in order to see the city. My SO is also coming along. Neither of us have been to Denver -- any favorite things to do/see/eat?

• We both enjoy art museums.
• I've heard good things about Wings Over The Rockies, but I'm not sure how it compares to other aviation museums across the country.
• Food: We are both kind of foodies, but it doesn't have to be fancy. Any cuisines to look for, or unique places to go?
• Natural things: We might visit Rocky Mountain National Park or something like that. We have a rental car and don't mind driving if the destination is worth it.