"Growing from the floor." Suggesting tree and mansion had been there some time -- but what did that mean?

"As far as I can tell at this early point, the salient points seem to be: One. The method of our arrival. No one seems to remember it happening or intend to come here." Conan paused to allow Ran or Hattori to contest this before continuing. "Two. The discrepancies in time. Three. The location and nature of this place. And four -- which is related to two -- the alternates."