Which idea came to the Dutch inventors first — building a wood-burning hot tub, or making it look like the bottom half of an orange pig? Whatever they were smoking, I'll take some.
The polyester tub holds 200 gallons of water. Attached to one end is a stainless-steel coil containing a stainless-steel basket that holds the burning wood. It uses convection heating, drawing in cold water from the bottom pipe and releasing warm water through the top one. To adjust the temperature, raise or lower the basket of wood. The tub can reach 104° Fahrenheit in 2.5 hours. There's a drink holder at the other end but, unhappily, no ashtray.
Not to bum you out, blithe bather, but downsides include emission of global-warming gases, the potential burn hazard if a stiff wind kicks up in the wrong direction, regrettable things you might say on your waterproof phone, and of course arrest for public nudity. Don't even think of using the product indoors. The price is $6,000 from Hammacher Schlemmer.