A torus can be used to model rotations of a sphere in 4 dimensions. Such rotations have two planes of rotation at right angles to one another. So one rotation plane corresponds to rotation around the major axis of the torus, and the other rotation plane to rotation around the minor axis. Viola, four dimensions. Neat, huh? Take a point (a,b,c,d). The major axis is then a^2+b^2 and the minor axis is c^2+d^2. That point then travels around the surface of the torus with one period of rotation around the major axis and the other around the minor.