You walk around the curved hallway, reach the middle and stop to turn around and look back. This part of the castle still seems darker for some reason, the curves on everything reminding you that you are in a perfectly round part of the building.

Now facing where the lounge door would be if it weren't for this door to the room in front of you, you see two doors to the left of you and a spiral stairway and a door to the right.

There is nothing behind you but wall and you can continue down the hall in either direction, feeling certain that the circle is completed on the other side.