User blog comment:Xilinoc/Ch. 566 (not out yet, but dis gon b gud)/@comment-24153155-20140129222822/@comment-24153155-20140130224945

Yes, you're right about that Hisagi mentioned that High density Reishi was spread all over Seireitei, but he also stated that he got lost due to the terrain being completely different (as the Wandenreich decomposed the Reishi the Seireitei is essentially made of). The Wandenreich was hidden in the Schatten Bereich, which is a dimension within that of the Seireitei. Shinigami are not able to see that hidden dimension, but they are able to see Reishi, so I kinda figured that the buildings that make up the Wandenreich must be made of high density Reishi (Quincy are known to be able to condense Reishi, so that would fit). It would even make sense that the high density Reishi acts like some sort of curtain, thus it could be (fairly) impossible for Shinigami to sense spirits of lower Reishi. But I guess the opposite should be true for the Quincy as well. For now, the only explanation I can come up with is that Schatten Bereich is still intact somehow, perhaps within (some of) the buildings of the Wandenreich, and that the Quincy need to decompose the Reishi in order to be able to fight the Shinigami, as it would somehow enable them to move between Schatten Bereich and Seireitei. This could be interesting as well, since it was slightly touched upon by Haschwald that Yhwach can't be outside Schatten Bereich for too long (chapter 514). Which makes me also wonder a bit how protected the Soul Palace still is. Speculations, speculations ;)