The Underground tours!!! So cool and spooky. Not sure about this particular company, but in general totally worth doing. Underground opium dens, prostitution, speakeasies and shanghaiing (see : http://en.wikipedia.org/wiki/Shanghaiing).
Pioneer Square, Seattle. This is where the Underground Tour is located, along with a Gold Rush museum nearby, and also look for a gallery called Flury & Company. They have extremely rare examples of Edward Curtis 100 year old photographs of Native Americans.