Diablo series creator David Brevik’s new/current ARPG is Marvel Heroes, and as part of that game’s ongoing second anniversary event, there’s a special drop that enables access to the “Classified Bovine Sector.” If you’re thinking that sounds like a Secret Cow Level, you are correct, Sir!
In the level you fight huge herds of cow-looking enemies, in super-hero fashion. A couple of screens can be seen below. Marvel Heroes: Secret Cow Level.
Update: Turns out this is not a new thing; it’s been accessible since shortly after the game’s launch, but has gained greater publicity during the current anniversary event.
Click through for a video of the level, because moo.