The Temple of the Winds by Terry Goodkind

TEMPLE OF THE WINDS is the New York Times bestselling 4th volume in the epic fantasy sequence The Sword of Truth. When the last of the wizards were faced with defeat at the hands of the agents of the Dark, they locked their most precious artifacts inside the Temple of the Winds for safekeeping. The Temple exists on a different plane of reality to either the lands or the Dark Realm, but as a terrifying plague is unleashed on the world one of the sisters of the Dark finds an unexpected gateway revealed to her. 

Richard and Kahlan will face their most difficult enemies yet as they struggle to find a way to combat both the plague that is killing their people and the threat posed to the Temple of the Winds. Prodded by prophecy, shadowed by betrayal, to complete his mission Richard must accept the Truth and find a way to pay the price the winds demand...before he and the world both perish.