One might think that the reference the cherubim in King Chizkiyahu's prayer means actual cherubim in Heaven; the Ralbag clarifies that the reference is to the golden cherubim that were part of the cover of the aron (ark) in the Temple. Chizkiyahu refers to Hashem as "G-d of Israel" - i.e., the One Who guides them with His providence - and "Who sits above the cherubim" - meaning the One Whose Presence is manifest in the Holy of Holies. (This verse is paraphrased in the prayer “You are Hashem, our G-d” in the preliminary morning service.)