God warns Moses to never let Aaron go behind the curtains that contain the ark, because that's where he's going to appear as a cloud. I don't make any of this up. Penalty: death.
Next, Aaron has to sacrifice a bullock and a ram. Then he has to get dressed, wash his hands and find two kid goats and a ram. Then he has to kill the bullock to atone for his sins. He has to throw dice down in front of the goats. One is for god, the other for the scapegoat. Hey, it was a real goat! The goat that gets god's dice is to be sacrificed, the scapegoat goes free. Then he has to fill the room with the ark in it with incense smoke so he can't see anything, then sprinkle blood on the mercy seat. Next, he has to repeat that with the goat. So wait, you can't sit on a chair that a menstruating woman has sat on, but god prefers to sit in bull and goat blood? Weird.
His next step is to atone for the sins of the temple and the congregation: he has to smear the blood on the altar. When all that is done, he is to bring the living goat to the front, lay his hands on it, and confess the sins, which are then transferred to the goat. The goat will then be released into the wilderness. Another bath, another sacrifice, more laundry, burn the remains, laundry, bath.
They have to do this every year on the tenth day of the seventh month, which is still the date of Yom Kippur. They also get to rest, but they have to deny themselves. And that's pretty much what happens now. For Jews. Of course, Christians don't have to because of Jesus. He certainly made life a lot less bloody, didn't he?