The Kuwadorian (九羽鳥庵, lit. "Nine Birds' Retreat") is the hidden mansion on Rokkenjima where Beatrice was held.
In Banquet of the Golden Witch, the existence of a smaller mansion called Kuwadorian on Rokkenjima is revealed. In the year 1967, Kinzo had managed to trap Beatrice in a human body and seal her memories. The human Beatrice lived in Kuwadorian alone. Rosa chanced upon this mansion one day, and invited the human Beatrice out of the mansion to "see the outside world", only to have the human Beatrice fall off a cliff and die. Upon her death, Beatrice regained all her memories and powers.