This is a remarkable piece of furniture. The concept being to design an environment in which to read and contemplate. Like the hull of a boat, the underside is curved, allowing steady gentle rocking, controlled by the occupant, as you would on a tree swing or an old rocking chair. This library can hold up to 400 books of varying shapes and sizes, and/or several hundred CD's, DVD's, or indeed nothing at all, it is entirely up to you. Oh, and no, it won't roll off, or tip over! The first two box sections adjacent to the base unit are flat bottomed - it would require a superhuman effort to even push it that far, after which there would be absolutely nowhere else for it to go. The movement is actually incredibly gentle and relaxing, especially as the ceiling remains static whilst you and the apex of the circles move together harmoniously. A wonderful sensation!