A place or situation with surroundings or events that would be better experienced high on marijuana. Some common stone-perfect environments include your local fair, the airport, the DMV/DOL and your place of employment.
Duder 1: "Why are we waiting in the parking lot?"
Duder 2: "Cuz me and Rich gotta blaze it up first dude. You down?"
Duder 1: "Sure I guess."
Rich: "That a boy!"
Duder 1: "Dude the fair is like the stone-perfect environment. Watch out dude there's some leprechauns!"
Duder 2: "Shut up man! I'm tripping balls right now."