With geothermal power – from natural hot (140 deg. F) water from an underground reservoir. The water (from Ice Age glaciers trapped by hardened lava from volcanic eruptions) is piped to radiators and hot=-water tanks throughout the city.
Geology
What a relief – this Geology category is exactly what you've been looking for, you stone-cold trivia champ. We'll be gneiss and say it: these questions rock!