A terrarium is nothing less than a miniature world - one that you can create yourself. It might be a tiny rain forest, with lush foliage and bright tropical flowers. Or it might not contain any plants at all. It might be made with crystals, feathers, bones, seashells, bits of wood, pieces of porcelain - anything that catches your fancy and helps create a mood or look. Whatever they contain, terrariums are the ultimate in modern, affordable, easy-care decor.