At 6th Avenue and Seneca over I-5, the aptly named <Freeway Park is a solution to the blight of a freeway roaring through the heart of Seattle [1]. Located just outside of the Washington State Convention Center, Freeway Park was built on a lid over part of that freeway and has greenery, waterfalls, fountains, and free summertime lunch concerts.
Links:
[1] http://www.moon.com/destinations/washington/seattle