Floating structures

I'd realy like to build a Waterworld style floating (or semi floating) water city. Or even the option of hovering cities, possibly kept up with rocket boosters (I'm thinking the flying fortress from Sonic 2 style! Either of these would be really cool. Especially if they sort of bob up and down by a few pixels to show the floating effect. That would be awesome!

 

What would happen if the rocket boosters holding up the city or whatever suddenly ran out of fuel :O

 

Then you get an epic metroid style escape sequence of course.