Adrian is escorted deeper into the levels of the castle in Hades. Just as Adrian surmised, the entire castle is made of Stygian Ore that repels the passage of the dead souls. This is to make sure that the dead do not wander around and hide inside of the castle or escape to the reincarnation cycle located inside the castle. Even Adrian does not know where or how the stygian ore is harvested due to it being an extremely kept secret in the underworld.
Due to the nature of stygian ore, the halls of the castle are obsidian in color, but they have this dark gleam that creates light that will illuminate the halls. It is not only the stygian ore that is noteworthy as there are numerous treasures that can be seen in the castle. Some are precious art or precious ores that would make any king or queen salivate from seeing them.