I love goldilocks threads precisely because they force me to look at a lot of different colleges from a brand-new perspective. For instance, it never would have occurred to me that Tufts didn’t have a clearly defined campus. I think the OP must mean something like the Claremont Colleges where each campus is separated from the city grid by a high wall, rather like a Yale quadrangle. Ironically, that would knock most of NESCAC out of contention. For, despite the fact that New Englanders - including, most famously, its favorite poet laureate, Robert Frost - have celebrated good walls making for good neighbors, very few of its LACs have them, preferring instead to hide in plain sight among the low-rise structures of small town life. Exceptions would include Trinity - but, then, in truthfulness, one would have to point out that the wall is there for a reason, the same reason Yale has gated entrances everywhere, to make people feel safer.
Less threatening immediate surroundings might include Smith which IIRC also has a wall, or at least a main gate, Barnard, and Vassar. These are all former women’s colleges for which a wall may have served a parietal function at some point in their histories.
Swarthmore, IIRC, is accessible only through certain carefully delineated entry points by car and then by foot (I guess, the train station would count as another entry point.) The same is true for the University of Richmond.