Stacey Kuznetzov made these fun robots that can traverse vertical metallic surfaces. Each bot is programmed with a unique personality and has embedded light sensors to perform some basic human interactions. She has an Instructable that explains how to make them. If you don’t have a metallic surface to infest with robots, you might want to check out the Waalbots instead.
I spent an afternoon once trying to convert a wind-up toy into a fridge-traversing creature, but didn’t have the proper magnets to get it to work. These autonomous ones look way more fun, and would be perfect for exploration if your floor space is limited. I’m thinking they could even drag a marker around their whiteboard pen.