Leviticus 16:18

And he shall go out unto the altar. — The authorities during the second Temple took this to denote the golden altar, or the altar of incense which stood in the Holy place over against the Holy of Holies, as this was the altar for which expiation was made once a year on this day (see Exodus 30:10); hence it was cleansed next. Beginning at the north-eastern corner, the high priest then went to the north-western, then the south-western, and last round to the south-eastern corner.