Why Cats Like Boxes

When I get something that comes in a large box from Amazon.com or somewhere, before we shred it for compost, it does duty for a few days as a cat castle. I'll sometimes cut slits in it so that they can reach out with their paws to slap another cat on the outside and, if it's large enough, I'll cut a couple of entrances in it. I have two 24 year-old cats who will lay siege to the castle when the younger one is inside.