Shunsui was in Hueco Mundo. His mission: Learn more about this world. He knew the risks, but he and the captain commander knew that it should be a veteran captain leading this expedition. He was wandering in what was obviously a desert. Hmmmm, seems normal enough he thought. This was his first visit in Hueco Mundo, so he wasn't sure what to expect. He was wandering in the desert for what seemed like hours until he saw the vague outline of a castle. So that's Las Noches he thought. Byakuya had told him about the castle. The closer he got the more he sensed a powerful reiatsu.