This tutorial will walk you through the process of building your own wood hot tub. The water is heated by a wood fire but you could probably choose a different type of heater if you wanted. I love the look of this hot tub because it is like a big barrel. You see a lot of diy hot tubs made out of plastic tubs but this looks cooler and more natural. ( at least I think so). It can seat 6 people and what i found fascinating was that after heating the water they went ahead and allowed the fire to burn out. Covered the tub over night in super cold weather and found that it had only lost a couple of degrees the next day, so once you get it hot it should be fairly easy to keep it hot. This hot tub was build in Finland where is seems many folks have hot tubs and saunas. I guess when it is that cold you need some thing to take the chill out of your bones. I know I would probably just go back and forth from sauna to hot tub.
This tutorial reads from the bottom of the page up so when you click over you may want to scroll to the bottom to begin reading. The tub was built and the tutorial shared by Experience to Share. He says pine is probably the best wood to use and I think it is cool that the wood swells with the water to stop any leaks. Neat build.