While visiting Denver over Memorial Day weekend, I walked from my downtown hotel to the lower downtown area and the South Platte River. I did not expect to see a revitalized waterfront with very busy bicycle paths lining the river along with new apartments and condos.
I had the same experience! I lived in Boulder before from 2005-2007, left, and came back in 2009. On my first trip back to downtown Denver, I was really impressed with the changes. The river is a much more prominent part of the city now thanks to that area, which is called Confluence Park (due to the confluence of the South Platte River and Cherry Creek).