The Citadel is an unmarked location in Horizon Zero Dawn.
History
Although the settlement of Sunfall was established as an army garrison during the reign of the seventh Sun-King Basadid, the Citadel itself was not constructed for many decades. During an inspection of the garrison by the eleventh Sun-King, the Radiant Marzid, in the sixth year of his term, the monarch was struck with a vision of an ornate palace and ordered the Sundom's resources to be redirected to building the structure.[1]