 What isn't something that the aliens control?
Within the dome of the barrier, it looked more like a well-kept if bizarre little country estate. They entered the house, which had no roof, continued to move beneath a sky that glowed with light which did not come from a sun or moon. It arrived before the meal, materializing against one of the seven walls of the roofless chamber. We seem to be in a universe of different properties as well as different dimensions. "They pass through their gateway to Earth at considerable danger and, probably, expense of some kind. As in all of this strange universe, excepting the dome-cages in which the captives were held, the training hall followed no rules of three-dimensional space.
 how the captives feel about being there
 how the captives feel about being there  what the captives eat  the captives' desires  where the captives live