If a forum thread on the Steam forums has found what some think its found, what you're looking at above is the first image from Portal 2.
RPS uncovered the pic, which shows a room in what looks like the Enrichment Center, showing the Companion Cube and then some.
It's been public knowledge for over two years that Portal 2 has been in the making. Former Valve member Kim Swift let slip there was a sequel on the way at GDC 2008, although chances are she may have also been referring to Portal: Still Alive for Xbox 360.
All this comes as Valve released a mysterious update for the original yesterday, adding in radio messages coded in morse.
Hopefully we'll find out sooner than later. Please?