I love the Shelter books! "There is something so sensual and real about natural buildings" YES YES YES~! I feel you on this so hard. Most buildings are just so human. It's a refresher to step into somethings nature created not ppl. Although as builders we can skillfully arrange elements to make us happy and comfortable.

The lack of codes here was a MAJOR draw to move (that and water, green spaces, low population, distance from cities and affordability...)

The wheels are a great way to skirt the issue. luckily wood is light and lends itself to mobility. OOO< get away with it. is there a outbuilding section in the codes. I know some places I've lived didn't require permitting for building less than say 30 sq m. I really hope you get to build the sauna of your dreams. Saunas are a much needed healing source for us all.