How's this for steam?
In 2009, a borehole drilled at Krafla, northeast Iceland, as part of the Icelandic Deep Drilling Project (IDDP), unexpectedly penetrated into magma (molten rock) at only 2100 meters depth ... – World’s first magma-enhanced geothermal system created in Iceland
I ran across the discussion of this in Wikipedia, and thought WOW! What if you had a whole city run on electricity from magma-powered steam generators?
The article is really interesting, and there’s more about the IDDP here on Wikipedia.
Anyhow, that’s where I got the idea as to how to power the city of Bridges.