The Sunhold is a fortress built within the Halls of Thunder to accomodate He-who-goes-before and his Red Ichorian guardsmen during divine election. That is it a fortress demonstrates the underlying antagonism that there is between the Great [whom He-who-goes-before represents] and the Imperial Power in whose domain the Sunhold is located.
The Sunhold is delved into the eastern edge of the Pillar of Heaven. It connects to the Encampment of the Seraphim by means of three well defended passages that culminate in double portcullises. Besides the barracks and the suite of chambers for He-who-goes-before and his attendants, the Sunhold also contains the Hall of the Sun in Splendour. It is here that He-who-goes-before holds court. The Hall connects directly to the nave of the Hall of Wings through the Sun-Eyed Door.
All of these locations appear in The Chosen. Specifically in the chapter entitled: “The Moon-Eyed Door”. It is here that Carnelian spends the long days before he discovers the trapdoor in the floor of the Hall of the Sun in Splendour which leads him down into the ancient halls and the discovery of the Library of the Wise and Osidian. It is in the Hall of the Sun in Splendour that Suth, his father, negotiates for votes with the rest of the Great. Note the promontary extending north-eastwards from the Hall where Suth and Carnelian stand looking down into the Plain of Thrones.