Valve announces plans to debut The Lab at next week's GDC, saying this will be a compilation of virtual reality "experiments" set in a "pocket universe" of Aperture Science, the hotbed of experiments from the Portal series. This will be offered free on Steam, and that's about all they are revealing for the moment, as you can see from the announcement:

Valve has announced plans to debut "The Lab," a compilation of new VR experiments, at next week's Game Developers Conference in San Francisco, CA. Set in a pocket universe of Aperture Science, "The Lab" offers multiple ways to enjoy room-scale VR. It will be offered free of charge via Steam this spring. More information will be made available next week at GDC.