Note i95 cutting across the upper left. The little spur coming down to the right is the off-ramp of Exit 22 (Brunswick). This off-ramp leads directly on to Route 1 North (Pleasant Street).
Here, we see where the off-ramp of Exit 22 (Brunswick) turns into Route 1 North (Pleasant Street). Continue along Pleasant Street, even after Route 1 North peels off to the left towards Bath. You're now on a 1-way street, headed towards Maine Street.
Now, you're still going northerly on Pleasant Street (a 1-way street), headed towards Maine Street. You can see, on the right side of the map, the T-junction where Pleasant Street hits Maine Street. Take a left at this T-juncture's light. You're on Maine Street, now, headed more or less westerly. Skip one left turn and take the second left. This is Cumberland Street, located between the Fleet Bank and the Maine Bank and Trust. The Keep is at Senter's Place, which is the second driveway on the left of Cumberland Street - the big, green building.
And here's that left on to Cumberland Street,
in between those two brick banks!