It actually is
kind of forbidden. For one thing, James isn't supposed to take
walks whenever he wants (he does it, anyway). On top of that, the woods around
the clinic don't seem to obey any sort of laws of nature. When James first goes
outside, for example, he observes, "[T]he land was shutting down and
preparing for winter and dying. Now it's shut down and prepared and dead"
(1.7.180). Only a day later, he says, "[T]he Land is showing life and
everyone wants to soak it in and appreciate it and remember it. Life. Remember
showing life" (2.1.208).
So, the woods are dead and dying when James is suicidal, and
stirring with life when his brother and friends come to visit. We guess the
grounds seem to mimic whatever James's mental state is at the time. And hey,
since this is pretty fictional, maybe the woods weren't even there at all. Who
knows—maybe the clinic is
Hogwarts! Watch out for giant spiders and centaurs, James.