Downtown Denver has a really neat mall set up for people to walk along and enjoy the moment. The 16th Street Mall is a place you can sit out on the patio and watch the sunset while sipping a brew or shop at Larimer Square for exotic items.
There are no cars allowed on the mall, only a free shuttle that runs all day and into the night. In the evenings you can also find the horse carriages strolling along the street picking up romantic couples.
Some of the more upscale places to eat include Wolfgang Pucks and The Cheese Cake Factory. If you go over a block you can go to the oldest hotel in Colorado: The Brown Palace. The Brown Palace has an elegant dining room in which even presidents have dined!
In Larimer Square you will find the little specialty stores. I personally like the Market which is a deli/gift store. The best part is the food as it covers many cultures and there are plenty of the best desserts.
The end of the 16th Street Mall is Union Station - a still active rail station. I say this carefully as it is nothing like the east coast stations, and has trains leaving only twice daily. The high ceilings and the dim lighting is a scene out of a book.
If you love books, just before the train station is the Tattered Cover. This is their second store, but it is four floors full of written treasures. Tattered is the biggest independent bookstore in Colorado and they have some great deals in their bargain section (perfect for the ride home, right?)