"Castles in the air" is an English expression that means dreams, hopes, or plans that are impossible, unrealistic. We don't have any of that around here, except occasionally about our Missouri state government. (OMG! 😖) We do, however, have a couple of small castles in the water. No half-witted medieval lord would build something so impractical.
Actually, they are disused water pumping stations in the Mississippi. (For some reason, we now get our water out of the Missouri although it has a lot more mud.) The background is the northern tip of the City of St. Louis proper. The outline of the city limits looks like a teardrop, which has some poetry. Anyway, the rapids you see in the background are part of the chain of rocks mentioned in Sunday's post.