When I was little, we lived in an older home and there was a little room under the stairs. It was just a little space that happened to have a door, but it became an apartment. A place to be that could be just about anything. I can still picture the upturned cardboard box and the wedge of smuggled (and dried out) cheese that made that little cubbyhole into a home. It even got an address.
Throughout my childhood, I always relished the space a blanket thrown over two chairs could create. The inside of my sweater became a tent containing a kitchenette.
An attic of an old church was converted to my one bedroom apartment.
It's been the same for my kids.
Last summer we got bunk beds and it just took a blanket getting accidentally draped over the edge of the top one to the bottom to get them hiding out.
The tree near our house is often a home. It's equipped with a complex pulley system for delivering laundry and food.
A pile of pillows and blankets can so easily be converted from slide material into a tent.