17 years ago, whilst on a trip to Norway, I had the chance to go in a very rustic hot tub. It had been built by the owners Grandfather and handed down to the Grandson. It was like an old whiskey barrel with a steel drum in it that had a chimney welded to it. The fire was made in the steel drum, and eventually the water was hot enough to get into. A couple of years later, whilst living in Scotland, I decided to try and replicate the Norwegian tub. The first prototype was a disaster, and took 3 months of swelling to hold even a couple of inches of water. The second tub had some major improvements, thicker wood, better construction, smaller diameter etc. and was able to at least hold water. The difficulty was finding a way of heating up the tub.