Cat's Tail is a tavern in the City of Mondstadt. Margaret is its proud owner and Diona is a bartender here. It is located between the Adventurers Guild and Good Hunter, though currently, it cannot be entered.
Since Diona was hired, between her cute looks and her magic touch that makes all of her drinks taste amazing, business at Cat's Tail has boomed.
In fact, she singlehandedly disrupted the monopoly Angel's Share once had over Mondstadt.