Klaus's mansion hosts the glamorous formal ball in season 3 of The Vampire Diaries.
The event takes place in “Dangerous Liaisons,” the show's 14th episode of season 3, which originally aired on February 9, 2012. Elena receives an invitation to a formal ball held at Klaus's newly renovated mansion. The party brings the members of the Mikaelson family together and gives the episode its elegant, dangerous atmosphere.
Esther Mikaelson organizes the ball as a celebration of her family's reunion, but the gathering conceals a much darker plan. She intends to link her children magically so they can be killed together, believing that this will undo the evil created by Klaus's transformation into a vampire. Elena becomes involved because Esther needs her blood to begin the ritual.
The mansion is associated with Klaus because he renovates and occupies it, even though the ball is a Mikaelson family event and Esther is the organizer. That distinction causes a common mix-up: viewers may remember it as Esther's ball or the Mikaelson ball, but the question asks whose mansion hosts it. The episode also features Klaus's flirtation with Caroline and the return of several Original family members.