When i think of calm i think of a babbling brook in a rainforest type area with birds and fish swimming calmly around a small pool at the base of the brook. You could do a landscape type center and as you build around the center get a little more busy but not enough to over energize. My father lives in a log house in the middle of the woods and his favorite place is by the brook and made a small area with a little bench to sit and continplate (didnt spell right)