Hand painted tree rings - would recommend putting all tree rings on a board (which could be painted a coordinating color to add pop to the art piece. Really neat idea for after school kids. Might just do 9 rings in a square frame!
Gravity Home: Sunday Inspiration The Church of San Giovanni Battista in Mogno, Switzerland. Designed by architect Mario Botta who created a pattern with layers of Peccia marble and Vallemaggia granite. (via Design Milk)