The department is now located at 574 Boston Ave, Medford, MA. Lat, Long 42.403674,-71.114193. You can see this location on Google Maps or MapQuest.
During regular working hours, only the doors at the north end are unlocked. Nights and weekends all are locked, so call someone to let you in.
From Davis, walk along College Avenue, slightly uphill, until you come to Powderhouse Sq, a large rotary. Go counterclockwise around the rotary, cross Broadway and exit on Warner St., which is next. Turn left on Boston Ave, go past most of the building and enter through the patio, or from the parking lot ifor theaf the patio doors are locked.
Turn left after you exit the turnstile, go up the stairs and catch the bus in the busway. Take the bus to the Powderhouse Square stop on the rotary after Warner St. and before College Ave. Walk out Warner St. to Boston Ave, turn left, and follow directions above.
From Harvard square you can also get the 96 bus inside the station.