There's historical trivia and architectural points of interest, as well as some bizarre entries like this one from user 'paugsburger,'
sometimes I drive, I love the view from 280 (at 6th and Townsend)Whatever.
The more time you give yourself, the more meandering the route this app returns. It's definitely designed to be used on an iPhone's web browser, but you can also launch it from your computer.
Check it out!