Park under Patriot's Square Park.   There are two entrances, one if you are heading South on First Avenue and the other if you are heading North on Central Avenue.  BRING YOU PARKING TICKET TO THE RECEPTIONIST FOR VALIDATION.  After you have parked, go down to the second floor of the garage and thorough the tunnel to the escalator.  Turn right at the top on the escalator and proceed to the second bank of elevators - 16th floor