Is it possible to isolate inner space from the need to see it as a volume from outside and to concentrate on the design of space itself? IN-SPACE is a web-based modelling tool especially conceived to give form to space, within space itself. With this tool, space is shaped from within, as we move through it expanding and contracting its limits. Starting from a cell located at the center of a three-dimensional grid, voids are carved by projecting the position of the viewer outwards along each of the three axes. As the avatar moves in this grid, space is being shaped. Conversely, voids can be undone projecting the position of a cell inwards towards the position of the view. Sounds, images and texts can be added to the cells that make a space. Once a space is created, the avatar can move inside the space or it can be driven automatically along the paths that have generated the space. Architecture students use this tool to develop their capacities of space conception as well as of space perception and orientation.