I figured that the IKEA hamster run might be the most extreme pet hack we'd ever feature on Lifehacker, but I reckoned without the determination of one woman to build a gigantic home for her pet rats.
The pictured rat run, as seen at IKEA Hacker, is built from the $299 Kullen wardrobe and a bunch of other tubing and boxes, so it's considerably more expensive than the pets themselves. That said, if you really love your pet rat (anyone feel a Michael Jackson moment coming on?), it's an impressive piece of work.
Rats chill at the Kullen [IKEA Hacker]