The details: Go outbound (West) on Beacon Street for 2.7 miles from Kenmore Square.
1.  Turn left from Beacon Street onto Chestnut Hill Avenue.  This large intersection is known as Cleveland Circle. 
2.  Turn right from Chestnut Hill Avenue at Dean Road, which is at the first light after Cleveland circle.  Continue for 1/4 mile.
3.  Continue straight at the intersection of Dean Road with Eliot Street.  The road curves to the right and its name changes from Dean Road to Crafts Road.
4.  Take the 10 o'clock turn at the intersection of Crafts Road with Reservoir Road.  This will keep you on the continuation of Crafts Road even though it looks like you are turning onto a different road (click here if you want to see a photo).
5.  Continue straight at the intersection of Crafts Road with Valley Road.  This sharply-angled intersection can be confusing; go straight; do not take the 10 o'clock turn (click here for a photo).  After 1.5 blocks you will see #27 on your left.