I've never thought of that but my grandson sure likes to build forts in the house. If he spies a couple of blankets, ottoman, and couch he just starts connecting the dots.
Personally, I reckon I like to install little "tree houses".
No kidding, I remember when I was in my very early teens my dad and his brothers used to talk about building tree houses right before deer season! That was 45 years or so ago. I envisioned big ol structures with doors, walls, roofs etc. When I saw the first one they were just a couple of support 2x4s and floor boards -- tree stands! They did build them sort of big though because they would sometimes go out the night before and sleep in them. They must have been anxious for opening day!