Cave Automatic Virtual Environment (CAVE) is a self-referential acronym. It was the first collaborative space where multiple users could interact in virtual space. The systems used at least three, though sometimes more, stereoscopic 3D projectors covering at least three walls a room. Creating life-sized 3D computer images, the user could walk through them. While stereoscopic 3D projectors are inexpensive today, at the time their extremely high cost, coupled with the cost of computers to create realistic images in real time, meant CAVE systems were relegated to biomedical and automotive research facilities.