There's a geothermal plant outside my town. Stinks like rotten eggs (but it smelled that way before since it's the site of a natural thermal spring).
Great energy source, though. Last I heard, the technology was at the point where they were trying to heat the water in an enclosed system (pipes carrying the water round-trip) to avoid the problem of corrosion and mineral build-up, which can be substantial.
I've visited a couple of hydrothermal pilot plants that were set up in the 70s-80s and those problems seemed insurmountable. Corrosion ate up metal as fast as it could be replaced and minerals continually blocked pipes and valves. This would be the best possible source of energy IMO if it can be perfected. Does anyone know how they're getting around those problems in Iceland?