So what do we know about The Builder of Monuments, as the architect was known? He was an architect of the Sixth Kingdom who lived several centuries before the Heretic King. The architect served the court during a time of scarcity and war. As a result, he was able to complete a number of significant projects, but not nearly as many as an architect of his quality would have been able to do in a time of peace and greater prosperity.
The Abode of Departure was a very expensive commission in a very remote part of the empire. This may not have been the original name of the structure, which was built to shield the Pharaoh's lands from from some chaos or danger to the north of The Abode of Life. It's primary patron in the royal treasury was the Pharaoh's Chief General. The Pharaoh's Armies provided the labor for construction.
The fortress-town was built with local stone to reduce the potential for weathering. The architect was equally attentive to local hydrology. The Builder of Monuments made the oasis-chain work for the fortification. Its structures draw potable water from deeper in the valley and store it in great cisterns deep beneath the fortress. This feature allows a defender to withstand a long siege in relative comfort.
The second faction were the hill tribes who made their home in The Abode of Life. Historically these peoples - the ancestors of today's Kirsi hillfolk in the valley - depended on trade with their settled neighbors in the desert and scrublands to the South. They resented the closure of their natural trade routes, and the disruption of their relations with kinfolk in the South. Some found their way into the community of the fortress-town, and carved their own secret ways through the town's cistern systems and aqueducts. So the fortress-town's security was never perfect.
The first is a vast chamber that today is called The Hall of Departure. Buried deep under the central palace of the fortress-town, this structure illuminates itself. It is well-guarded and said to be a Gate which opens onto an infinity of other Gates.
The second hidden structure is simply known as The Sanctuary. The Kirsi say one is cursed to even utter its name or to inquire in any way about this structure.
The third structure is a vast mechanism built according to secret spell diagrams drawn by the Priests of Thoth. This mechanism was designed to come to life if the fortress-town was ever taken by invaders. In that contingency, the mechanism would open a vast sinkhole beneath The Abode of Departure; desert sands would swallow it whole.
The question is why this hasn't happened already? First the town was taken by an exiled General of the overthrown Heretic King. During the Long War, The Abode of Departure was the first stronghold of the Eternal taken by Kirsi warriors. It remains in Kirsi hands to this day. The question remains whether the town is living on borrowed time, or if the ancient mechanism somehow has sand in its works. Time will tell.