"a world unto itself" = a world of its own

Itself: Is used to emphasize that you are referring to one thing or type of thing but not others. example: English itself has become international language.

To me, it emphasizes that the thing has become so different and self sufficient that it is like a different world, figuratively, completely separated from everything else in its actual existence. In the example you give, the camp is so separated from the problems & everyday life of earth, that the camp might as well be on another planet, or its own planet.