I love dens. Always have – as a child I would spend hours in the garden with my brother and sister, collecting large branches, reeds, planks of wood – anything to make a den with.
I think the joy was being able to create something from nothing. (I also suspect that I had an enclosure schema going on. Even now I like to sit in the corner of a café, tidy things into boxes and prefer grids to mind maps).
Of course, once you have an enclosed areas such as a den, you can invite others in – or shut them out. The element of self-choice can be very important to children. Sometimes even well meant adult intervention can be disruptive or even destructive to children’s play.