The Castle, just like many other ancient Castles that existed years ago, had a maze of secret tunnels which led the rooms in the Castle in case of any emergencies where they would have to flee.
What made the North-East secret tunnels different from any other tunnels was that in the middle of these tunnels, they had safe rooms which, just like the name, had cocoon walls to shield the inhabitants from any danger.
The rooms were built specifically for an unseen war where they would need to hide the women, children, and elders from the eyes of the enemies.
Xavier, after his emanation of being the King, was the one who made these rooms for those specific reasons and they were so advanced that they could withstand explosions to some extent.
So when an emergency like this one broke out, Ren was smart enough to lock his wounded wife in one of these rooms with the head maid, Evalet, to take care of her when he wasn't around.
