Thanks for checking it out.
The riddle is a trick. There is no riddle. The fairies there are having a laugh at the PCs, convincing them to waste time in the library.
I may need to make the entry points clearer. On the map it states "Master Bed Staircase: Up to Private Tower" and it mentions being able to climb to the tower as well. I've seen a lot of modules color code points of transition and such and I may begin doing the same.