any size dose (well keeping it sensible, i dont think i would ever do more than 600ug deliberately), anywhere. walking in nature is fun whether on 50ug or 400ug. Same goes for being in a psy-trance rave/rock concert, friends house, staying out in a field with a fire going all night, hippy gathering whatever. The only places i wouldn't do it are in school or in a rough neighbourhood, the bad vibes might freak me out.
Depends on the time of year, out side in nature is great during the warm season. Getting lost in a forest, walking near lakes etc... At home is fun too.