Sure, this robot is an "art project," but it's still pretty damned creepy. It's called Zwischenräume, and it hides in walls only to punch through to check out what's on the other side.
Here's the artists' description of how it works:
The installation embeds a group of autonomous robots into the walls of a gallery. They punch holes through the walls to inspect what's outside, signal each other, and conspire. As if the walls had ears and a hammer to pierce holes for their eyes to see.
Oh good, wall-punching robots that "conspire!" What could possibly go wrong?! I'm glad this is confined to an art gallery, although I will say that installing in a buddy's wall would make for a hilarious (and very expensive) prank. See it in action below.