Kiamo Ko is a castle located on the peak of Knobblehead Pike in the Vinkus. The fortress is the home of Arjiki tribe chieftains: the Tigelaar clan. It is a location that is featured both in the novels and the musical production.
In both book and musical, Kiamo Ko is where Elphaba has her final stand-off with Dorothy.
In the Novels
Kiamo Ko serves as the home of the Tigelaar family: Fiyero, his wife Sarima, their kids Irji, Manek, and Nor, and his sister-in-laws. Years after Fiyero died Elphaba Thropp arrives here on a caravan accompanied with a mysterious boy named Liir; later, Nanny arrives to stay with the two. Elphaba stays with the family in the castle until they are arrested and killed by Commander Cherrystone's Gale Force; thereafter, Elphaba lives a hermit lifestyle alone with Liir and Nanny in the castle. During this time she begins to be known as the "Wicked Witch of the West", as she begins to study magic from the Grimmerie almost obsessively until her ultimate demise by the hands of Dorothy Gale.
Ever since Elphaba was killed and Liir left with Dorothy, Nanny has been living alone in the castle under the care of Chistery and the other flying monkeys. Nanny is briefly seen in the castle when Liir returns to Kiamo Ko. She is becoming very senile in the mind and the castle is in a bad condition, until Liir sets the castle right before leaving again.
In the last book, the castle is still being lived in by Nanny and she has a brief conversation with Rain, who she confuses for Elphaba because of her dementia.
In the Musical
In the musical, Fiyero does not have a wife or children, and Kiamo Ko is described as simply his family's "castle in the Vinkus", which is abandoned as they live in another castle elsewhere. He and Elphaba plan to go there to escape the Wizard's royal guards. Only she is able to go, and she takes shelter there, holding Dorothy Gale hostage.