I once witnessed a cubicle on wheels speeding down the curvy roads of Mt. Tabor loaded with office supplies and a few “employees” armed with squirt guns blasting the crowds of screaming onlookers. It was all part of the Adult Soap Box Derby– an annual PDX tradition that gathers artists, scientists and a few thrill-seeking maniacs to careen down Tabor in their homemade soapbox inventions. Saturday marks the competition’s 20th year. Races kick off at 9:30 am and run until “4ish” with the final 3-car race for all the glory. There will be food vendors, thousands of spectators, a whole bunch of hay bales to catch runaway cars, and a dazzling display of Portlanders’ creativity (mostly PG-rated.) Bring a picnic!