The Palace of Sinew is the prison demiplane of Dyrrn, the Corruptor. Like all of the Daelkyr imprisoned in Khyber, Dyrrn has molded their demiplane to fit their preferences. The Palace of Sinew is a nightmarish work of art, the entire demiplane sculpted from flesh and brain matter. Dyrrn has arguably had more of an impact on history than any other daelkyr, and is responsible for a wide variety of abominations. The Palace of Sinew is a monument to this, a vast collection of draft works of "art" and rejected scraps.
Within this grisly museum is the nervous system of Dyrrn's activities in the world, maintained by a network of elder brains that relay the Overmind's orders to its minions.