Easily the best building I have ever visited. Radical, but not out of place, it is filled with surprising and incredible spaces. It was designed by superstar architect Rem Koolhaas and lives up to his reputation for being one of the best. An audio-tour mp3 can be downloaded from the Seattle public library website for free. It takes about 30 minutes and gives some valuable insight into how the building was designed and functions, as well as ensuring you don't miss any of the hidden gems.