Maybe you just moved and your home is full of cardboard boxes. You're feline pal thinks this cardboard fortresses are all for him. He'll hide behind them, nap inside them and scratch at the corners. This may leave you wondering why cats are so obsessed with what you see as garbage.
There's a reason why you've heard the phrase “curiosity killed the cat.” Kitty is naturally inquisitive and any new addition to his home will be given the once over. This is because your home is his territory. He'll routinely patrol his home looking for anything new or interesting. This is why Kitty prowls around the house and sniffs and paws at your stuff. To him, it's not your stuff at all, it's his stuff. Since his territory is where he lives and hunts, he wants to mark and memorize every inch of it. When you make a big change, like moving or having a big empty box, he has to make sure he approves and lets everyone know it's his.
Safe and Sneaky
Curling in a small, enclosed space makes Kitty feel safe. He can comfortably nap here without having to worry about uninvited guests sneaking up on him. This could be in the form of a fluffy bed you've bought him, but he'll be just as comfortable in empty box. Kitties also like to watch their environment and feel invisible. His wild cousins will lay out of sight from potential prey. In the wild, you could right by a leopard and never know he was there. Kitty thinks he can do the same thing. He'll take cover in a box, or under the bed and spring into action when he feels unnoticed. A cardboard box offers dark, enclosed space where he feels both safe and sneaky.
The Need to Scratch
You know Kitty likes to scratch stuff and boxes provide an excellent opportunity to put those claws to work. Kitty will scratch to sharpen his claws and mark his territory. He has glands between his paws that leave behind his scent when he scratches as well as leaving a visible mark to others in the area. Cardboard is a perfect medium for scratching because it can easily be dug into with his claws, kind of like the bark on a tree. A tall, heavy box allows him to completely stretch out and get a good grip, the same reason the couch is a favorite for scratching. Kitty needs to scratch so get him a good sturdy post to channel his urges to a less messy and destructive place. Covering it in catnip and rewarding him with a treat will teach him that his post is a safe place to scratch.
Kitty's love of boxes shouldn't dismay you; it's an excellent opportunity to give him a cheap toy he'll adore. Throw a pillow or towel inside and set it near a window. He'll appreciate a warm, quiet place to nap. Flip it upside down and cut holes on top or the side and Kitty will hide inside. You can build him a condo by fastening some boxes together and cutting holes for him to travel through. This is a cheap way to build Kitty his own fortress he can nap in, hide in and destroy to his heart's content.