Hello everyone. I just purchased Shadow of Nerekhall. It comes with some 2x2 hallway connector tiles, the ones that allow a transition from an A sided tile to a B sided tile. Those tiles have a yellowish green ellipse on them as wide as the hallway. Some other room tiles have the same ellipse. It kinda looks like a "mystical door", but I didn't see any description of it.
Is this an obstacle or a hazard? Or is it just artwork that does not affect gameplay?