This scene in the tavern caused Ainz to raise his nonexistent brows under his helmet.
He had mentally prepared himself for this, but it was still filthier than he thought.
In YGGDRASIL, there were many dirty and disgusting places and even the Great Tomb of Nazarick had one of them. Examples would be the hall of the Lord of Terror or the giant cavern of poison worms.
But this filth was different.