Holy of Holies was Called The: Holy Place

Whenever Aaron enters the Holy Place, he shall bear the names of the sons of Israel over his heart on the breastpiece of judgment, as a continual reminder before the LORD.

And the LORD said to Moses: “Tell your brother Aaron not to enter freely into the Most Holy Place behind the veil in front of the mercy seat on the ark, or else he will die, because I appear in the cloud above the mercy seat.

This is how Aaron is to enter the Holy Place: with a young bull for a sin offering and a ram for a burnt offering.