Alternately "Kimball Farm Ice Cream at Bates Farm" or "Kimball Farm Carlisle" (there are a couple of others including the huge place in Westford with Miniature Golf) this is one of those that you stumble on when driving through "back roads" but still trying to get somewhere - it's on 225, not far from the Concord River (which serves as the Carlisle/Bedford border.)
Lots of parking and some kid-oriented farm entertainment (literally, they have goats.) Picnic tables, some shaded; they also host a Farmer's Market on summer weekends.
Good dense ice cream in traditional flavors; I stop in when I happen to be relaxing on those particular back roads (the Bedford Boat Ramp is actually a good birding spot when there isn't a lot of boat or fishing traffic.) Most recent visit: ½ Butter Crunch and ½ Maple Walnut, solid classics; my friend had a Strawberry Ice Cream Soda. (Their menu also includes Vegan (coconut based) and Sugar-Free options, which I will not be reporting on further.)
It's one of your New England classics - you might not have been looking for it, but if you drive by and think "Hmm, I could go for some ice cream" you will not be disappointed, and it's big enough that it won't be too crowded in the summertime. I've been stopping at Kimball Farms on and off since 2007, and was there most recently this past weekend.