No-electricity hot tub

This hot tub of Dutch design uses a coil around a fire to heat and circulate water from the wooden tub. No electrical hookup required!

After filling the tub with water, a fire can be started in the attached basket to kick start the heating process. The hot water starts to rise in the spiral, which automatically starts pouring in through the spiral, and begins circulating from the bottom to the top. The temperature is adjustable and to warm 700 liters of cold water the tub takes around two and a half hours.

DutchTub, designed by Floris Schoonderbeek, via Core77.