This excerpt taken from the HPQ DEF 14A filed Jan 29, 2008.
From Points North via I-93:
Heading southbound on Interstate 93 Boston, take Exit 23, Purchase Street and move into the left lane. At the top of the ramp, take a left turn onto the Evelyn Moakley Bridge/Seaport Boulevard. Follow Seaport Boulevard for approximately .8 miles, the Seaport Boulevard entrance to the Seaport Garage will be on the right, after the Seaport Boulevard/B Street intersection.