Threrdsul was the research facility where the Stagstbur Research Group, headed by Stastn, was stationed when the The Great Plague hit. It became the headquarters of the Scions for a time, until they all went their separate ways, determined by their individual patrons.
Threrdsul was buried deep within its stone foundations in 293 BCT, 25 years after the Great Plague. Loshm did the work at the recommendations of Stastn and Zhosis. The Scions had largely abandoned the facility but they wanted to preserve it so that they would have a place to retreat to should it ever be needed. Any of the first twelve Scions can enter the facility from a specific location on the surface.