Bridge at Rio Salado and Central Avenue, near the wonderful (yet in terrible need for more visitors) Phoenix Audubon Center. This bridge, if you've ever been underneath it, has giant concrete pillars, probably 35 feet high and 100 feet wide. This is one of those "why didn't we think of this before" opportunities. Put rock climbing features on these pillars. If the city can have a skate park, or allow people to ride bikes and inline skates in parks, or go hiking in any of our mountain preserve parks, the city could create something like this... statistically, it would be safer than any of the things I just mentioned, but what a cool amenity would this be. Total investment would be next to nothing - the project could be started with $10K and be pretty amazing with just that much investment. What other city offers something like this?!