This paper describes in details the implementation of the ActiveCube system. ActiveCube allows users to construct and interact with 3D environments by using physical cubes as bi-directional interfaces. A computer recognizes the 3D structure of the connected cubes in real time by utilizing a real-time communication network among the cubes. ActiveCube is also equipped with both input and output devices that are integrated in the cubes and help in making the interaction intuitive and clear. Spatial, temporal and functional consistency is always maintained between the physical object and its corresponding virtual representation. Experimental results demonstrate ActiveCube's potential in achieving natural and intuitive interaction.