Good eye. This place is rather dark, so it's hard to make out any structures.

[Before the light from the doorway fades, she pulls a makeshift map out of her pocket and unrolls it. The map looks like it was drawn by a group of children, illustrating different purple and blobby shapes hovering around the stairs and narrow corners of the tower.

When it comes to unusual creatures, sometimes children see things other adults are oblivious to.]

We might be onto something in that area since these ghosts like to stay hidden.