KW spends some sort of time with every box that comes into our house - and since I shop mostly online, there are many! They have a short life span, though. Last week, she put my sandals inside a box and tried to carry it upstairs. It was too big and unwieldy, though she managed to carry it from the kitchen to the bottom of the steps. She eventually gave up, and it is still sitting there for me to break down.
Here she is playing peek-a-boo and then climbing in (the all-time favorite box game).