As one of Google’s “April’s Fools Pranks”, they’ve enabled Anaglyphics Red-Cyan stereo on Google Street View.  Simply load up street view as you normally would, and you’ll see a new icon there to enable it.

In reality, it looks like they’re just duplicating and shifting the existing image a bit, it doesn’t really add much depth.  Also, they leave the existing colors in the image with can create some distracting effects.  But it’s a fun little trick, and worth playing with if you have some anaglyphic glasses lying around.