One city using a lot of geothermal energy already is Beijing. In this video, you can learn a bit about how geothermal works, and about its use in China. Bonus: silly rapping about geothermal thrown into the middle of the video (not quite as good as the "Double Panes" version of M.I.A.'s "Paper Planes"). Thanks to Alex Pasternack of Treehugger for finding this one.