Barney Calhoun and Rosenberg reach an older part of the Black Mesa Research Facility where a disused teleporter system is being reassembled by scientists. To make the teleporter completely operational, Calhoun is forced to travel to Xen and activate a device to allow teleportation to happen. Notable in the older part of the facility is older-looking models of health and HEV chargers and the use of hand scanners instead of retina scanners for identification.
The remainder of the game takes place in an abandoned, walled-up sector of the base originally built for research of the first teleporter device. Calhoun, Rosenberg, and two other scientists (Walter Bennet and Simmons) try to restart the prototype teleporter. Calhoun is briefly teleported to a ruined human research camp on Xen to operate a triangulation device.
