The third structure, GBB III, was initially designed as guest quarters. Before it was added on to, it was barbell-shaped, with two octagonal bedroom pods joined by a square bathroom space. Here, a three-dimensional tartan grid and proportion were the organizing principles. The grid is employed to shrink the small rhombicubotahedron to a size more suited to the bedroom function by reducing alternate squares to 1x√2 rectangles. 

Work on the third structure was precipitated as a sideline of Chris' job as an architecture professor. He led a group of Mississippi State University architecture students in 1989 on a study program, and they began erecting the structure; a second group from North Carolina State University/Rice University in 1992 continued the work. It was completed with the help of a local crew of workers in 1994.

The two bedrooms are organized spatially in contrasting manners. In one, three single beds are built-in along three walls, leaving the center of the room open, while in the other, a double bed thrusts to the center, with space around it. This object/space contrasting relationship is also encountered in GBB I, with the dining table occupying the center of one pod, while the kitchen counter and sitting bench line the walls of the other.

When we decided to upgrade the compound for winter habitation, the GBB III double-bed bedroom was designated as the Master Bedroom and a bathroom/closet area was added to it. One reason for choosing this room was that it was easy to add on to.

The addition, built by Christos and a hired handyman, Giorgi, following our retirement and relocation to Greece in 2001, comprises a corridor with sink, countertop, space for a washing machine, and closets, leading to a bathroom with toilet, bidet and a "shower tower," with colored skylights.