Abstract: A graphical user interface permits navigating through a plurality of stacked window layers or image planes. In one form, moving through one image plane to an image plane below simulates pressing on an elastic membrane until it bursts. In another form, worm holes are used to access selected layers at different depths. In another embodiment, a property analogous to thickness, is associated with an image plane and the amount of time or force required to pass through the image plane is controlled as a function of thickness. In yet another form, a force feedback input/output device having three degrees of freedom is used to give a user the feel of physically penetrating through plural stacked layers.