You spend your workdays inside, behind a desk, breathing stale air and drinking acrid cofee .  Here's an opportunity to clear your head on your way to work or on your way home.  Shoreline Water Taxi is offering free boat rides during commuter hours between the Sears Tower and the Michigan Avenue bridge until May 15.  Ride for free in the mornings from 7:00am until 9:30am and the afternoons from 4:00pm until 6:30pm.   Now that's a nice alternative to the bus!