Concept:

An entire floating city, built on top of a massive, solid foundation slab, held up like a puck on an air hockey table by thousands of small, intermittently firing geysers. It’s built that way because there are earthquakes at least every few days, and this keeps the quakes from touching the city. They’ve built in jets to provide extra lift if needed, but there’s nothing to stop the geysers, so the jets haven’t been needed yet.