All the Land is sacred, but what makes it so is that it holds within itself the continuation of the Ancestors... the Underworld as "primal land", the purest essence. The creation of a sacred space is making an alignment or attunement between a physical area and this Primal Land of Ancestors. Hence the ideas of "place that is not a place, time that is not a time", or a la Holdstock (Mythago Wood, Lavondyss, etc), "the place where men's spirits are not bound to the seasons".