Walking (~25 minutes): View Directions in Google Maps
Leaving Harvard Square Station, make a U-Turn so that you are walking back up Massachusetts Ave (against the flow of one-way traffic). You will want to be on your left-hand side of the road when the road forks, staying to your left, which turns into Harvard St. You will soon approach Quincy Street on your left. Turn left onto Quincy St., follow Quincy all the way to the point that it makes a T with Kirkland St. Turn right onto Kirkland St. Follow Kirkland (which turns into Washington St.) through the intersection with Beacon St. At the next stoplight, turn left onto Dane Street. You will find Greentown Labs on your right at 28 Dane St., just after passing Tyler St. on your left.
Bus (~15 minutes): View Directions in Google Maps
At the corner of Massachusetts Avenue and Garden St. board the 86 bus toward Sullivan Square. Get off at Washington St. @ Calvin St. Make a left onto Dane St. and Greentown Labs will be located two blocks down on the right.
The nearest Hubway bike is at the corner of Beacon St. and Washington St. Walk up Washington St. one block (past the Wine & Cheese Cask), make a left onto Dane St. Greentown is two blocks further on the right.