Enclosed skywalks between office buildings, as seen in downtown areas. Based upon the visual similarity with hamster habitrail tubes. Often shortened to simply "habitrail."
When a man (usually gay) inserts a habitrail tube into his anus with the goal of luring a small rodent (ie: gerbil, hamster, guinea pig) into his rectum to enjoy some sort of bizarre combination of sexual gratification and animal cruelty all at once.