I just wanted to share this site with you.
http://www.wildsidepdx.com
It shows you what to do while on layover.
Almost all of the cities listed are done. I talked with the owner of the site and she said they will be listing 70 US cities. The cities were chosen by how often we fly into them and end up on layover. Almost of all of the activities were chosen for us, the others were selected for the natives of that area.
Might be worth checking out. Scroll down to see the city list.