An airy room, though, threatens to float away. It's important to ground it with a weighty architectural element, like a stone or concrete fireplace. We chose concrete for its contemporary look.

At about $20 each, 20 mosaic stepping-stones kits were certainly cost prohibitive so instead we bought three bags of concrete masonry mix with sand for $3.65 each at a local home-improvement store.

Children would make stepping stones of Baskin Robbins ice cream cartons, by filling them with cement and decorating them with marbles or shells. "It's a usable stepping stone they can plant in their ...