The idea of a gateway to Another Dimension is quite old. Sometimes the dimensional gateway would appear to be a mirror or book. A computer is both of these. "Cyberspace" is the dimension it opens. Rather than go Down the Rabbit Hole into a Spirit World, the character puts on some VR goggles, plugs an Ethernet cable into his skull, or gets "digitized" into data. What do they see when they go online? A pretty nifty 3D world, designed as a Viewer-Friendly Interface made up of Holographic Terminals.