It was very old, and even larger than the Protector's Palace. It was a massive structure of native Grayson stone, built when fortresses were still needed against enemies as well as the hostile environment.
The Steadholder's personal office was held in spartan simplicity. William Fitzclarence's father and grandfather added some tapestries and paintings to soften it, but Fitzclarence removed them again. (HH5)