A little boy and his older sister explore a dark forest ``looking for a creature of enormous size, with a backbone as strong as a beech tree...and thighs as round as oaks.'' While the text mentions such pleasurably shivery possibilities as the scent of a moist bank being ``the giant's mossy breath'' or wind-blown brambles his snare, the illustrator's marvelous watercolors offer more evidence of an elusive giant, and perhaps other weird creatures, in the forest's shadowed recesses, the twisted, muscular shapes of trees, and some startling juxtapositions of fungi and knotholes. Meanwhile, friendly, exquisitely rendered birds and squirrels and a family of foxes lighten the gloom. The beautiful art tantalizes the imagination, yielding intriguing new images with each rereading. (Picture book. 4-10)