As far as small structures go, tree houses are my favorites. Walking in my neighborhood the other day I saw one up in a tree, and I suddenly remembered how much I liked them when I was a kid. My brother, sister and I would gather whatever pieces of wood we could find, nailed them against each other on four sides, put a cover on top, added a few pillows inside, and it became our sanctuary. Never mind that spiders would find it just as comfortable as we did.
It doesn't really matter how they're built I think. As long as they have the essential elements: small space, nature, and a sense of self-reliance, the magic is there. I was looking for a subject to make a series of collages, and well I found it, tree houses! The ones I'm using as inspiration are put together much better than the one of my childhood, but they all have the same playful spirit.
My first one is based on the treehouse on stilts designed by the architect Terunobu Fujimori. It looks like it's going to walk away, I love it! Its japanese name is takasugi-an, which means "a tea house [built] too high." In japan the tea master traditionally has control over his own teahouse and builds it himself without an architect or skilled carpenter. That's what Fujimori did (although he is the architect).