^^^ I got back into shape climbing the hill from Mass Ave to this park. In fact I arrived probably an hour after you took those pictures. Usually I park my car near the Stop and Shop on Mass Ave to give myself a few minutes of a warmup walk before I get there. The (soon to be famous) Arlington Triple for 730' is as follows, all starting on Mass Ave and crossing Gray Street midway:
Robbins to Robbins, ending at far side of Hawthorne - 230'
School to Kenilworth, ending at far side of Hawthorne - 230'
Menotomy to Grandview to Eastern, ending at the giant stone water tower - 270'
My record for the triple summit (includes the short warmup walk and 2 full descents back to Mass Ave) is 46 minutes, but anything under an hour means you're working hard. It's approximately 3.2 miles for the triple summit and 4.2 total when including the trek back to the car. The park closes at 9 so best bet is try to finish the last climb no later than 8:45 so you can descend through the park, cutting through at Coolidge Road. Try the double for 500' (leaving out Robbins) if the triple is too much. Robbins is both the easiest of the 3 streets, and the one with the most dangerous uneven sidewalks, but I still prefer to knock off all 3 when I have the time and the energy.
Unrelated, here's some pics from 5/27.
IMG_0697 by
David Z, on Flickr
IMG_0700 by
David Z, on Flickr
IMG_0742 by
David Z, on Flickr
IMG_0769 by
David Z, on Flickr
IMG_0775 by
David Z, on Flickr
IMG_0903 by
David Z, on Flickr