BTW, Stage 4 in Super Castlevania IV is the Outer Keep only in the Nintendo Power SNES coverage.
Based on the OST name, the stage layout, and what happens in the stage, it's some sort of "Mansion of Tricks".
"Trick Manor", "Clockwork Mansion", and "Spinning Tale", lead one to believe it's a type of large mansion on the outskirts of town, not all that dissimilar from "The Villa" from CV64, only with many tricks played on the perspective of the intruder, accomplished through clockwork movements.
This is how the rooms rotate, and other rooms spin, and other rooms have crushing grindstones; clever clockwork tricks.
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It seems that the natural and made-made elements in the vicinity of the Castle are swallowed up by the Castle itself. This is why in CV64 there's a "Villa". The villa is called the "Castle Annex". So there was already a villa there, and when the Castle begins to materialize, it just engulfs the area.
Headcanon: Any good people, animals, etc. engulfed and destroyed by the walls of the castle become lost souls, which inhabit the torches and candles of the castle.