Map your favorite vibrant places in Foursquare
Right, I'm a foursquare user. And I know I have used it as an example in other challenges as well, but here it is such a good fit again. The list functionality allows you to collect vibrant places and share them with the world.
As an example, here's a list made by my friend
The Riga Talk Walk guides you through one of the nicer parts of Riga. There are probably other examples out there, but this is a very easy and effective way to promote the vibrant hotspots in your town. Both for locals as for tourists.