Take the MBTA Red Line to Kendall Square. Come out so you're facing the Kendall Square entrance on the opposite side of the street. This is Main Street. If you came from the north (Harvard Square, Alewife, etc), follow the sidewalk to the left; if you came from the south (Park Street, Ashmont, Braintree, etc), then cross the street to the other entrance and follow the sidewalk to the right. You'll pass a fire station almost immediately, and then you'll come to Ames Street. Vassar Street is the next street after Ames, but it's been under construction for some time; the entrance to the East Garage is in the parking lot in the middle of the block between Ames and Vassar.
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Take the Massachusetts Turnpike to Cambridge (Exit 20). Follow the street from the offramp and continue straight until you reach Central Square, and take a right onto Massachusetts Avenue. Follow Massachusetts Avenue to Albany Street, and turn left onto Albany and then right onto Main Street. Pass through the first set of lights on the corner of Main and Vassar, and park in the East Garage parking lot just after Vassar Street.
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Take Memorial Drive towards MIT and Kendall Square. Turn onto Wadsworth Street, near the easternmost part of MIT. At the first street after that, turn left and follow it to the end. At the end, turn right onto Ames Street and follow it out to the first set of lights. This is Main Street. At this point you've passed the lot on your left, but there's a barrier down the middle of Main Street. Make a U-turn at the lights, then park in the parking lot.