Abstract: The device utilizes a changeable-configuration geometric arrangement including a plurality of units, such as tetrahedrons, connected together at points by means of joints. The tetrahedrons can be equally divided into two different types of units that are exact mirror images of each other. The unit in each type has four triangular faces. The units along with the joints form an articulated chain in which any two adjacent units are of different types. The assembly of any two units connected together with a joint allows both units to rotate relative to each other in all directions around the center of the joint. In the articulated device, six consecutive units can be used to form the configuration of a cube. Different coloring and/or numbering schemes can be used to provide different levels of complexity and challenge for the puzzle. Units can be formed as right tetrahedrons having two faces with side lengths generally equal to (L, .sqroot.2 L, .sqroot.