Watched a german documentary about this. They said that they need to open the upper windows when the sun shines, otherwise it will get too hot inside.,(reply>), @Tom P. we visited it in the middle of winter. it was -20C outside but i still couldnt fall asleep from the heat and humidity inside.,(reply>), @Bern It is. I remember not being able to sleep because of the heat there.,(reply>), @MarsToRover because one of them is the mediate climate rural Brandenburg and the other is a tropical island with waterslides and a balloon,(reply>), But why would you go there when the sun shines anyway,(reply>), jesus christ, must turn into a sauna or something if they dont open the window