Holy of Holies: God Appeared In
Source: TTT
Exodus 25:22
And I will meet with you there above the mercy seat, between the two cherubim that are over the ark of the Testimony; I will speak with you about all that I command you regarding the Israelites.
Leviticus 16:2
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.