(Spacing = 2-5-2-5-2-5)
(bottom left to right)
SHADOW BOX is a continuous design, and requires tiling. The fun part is to come up with some sort of spontaneous or artistic fabric pattern, not heavily organized, so as to offset the almost extreme grid control in the boxes. A shadow box is an enclosed glass-front case containing a collection of objects. To "Shadowbox" is a form of "phantom" boxing, used as an exercise routine. There's something humorous about it, according to Wikipedia, "In shadowboxing, the participant throws punches at no one in particular."
According to Jinny Beyer's QUILTER'S ALBUM (p. 271-9), the design, with 3 x 3 boxes (see upper right) first appeared in the Aunt Martha Series, Patchwork Simplicity, about 1977. Barbara Brackman's ENCYCLOPEDIA OF PIECED QUILT PATTERNS, illustrates the block with 2 x 2 boxes, flips the dark/light arrangement (see upper left), and traces it back to "Peterson's Magazine" under the name, NEW PATTERN, 1857 (#1366), and later as SHADOW BOX in the Nebraska Collections, a 1975 exhibit.
Compare at this site with CUBE LATTICE, or ON THE SQUARE, also AUNT MARY'S DOUBLE IRISH CHAIN and SHIFTING CUBES.