Hard to say really.

[He moves along with Darin, providing him with ample light while also looking around the space at the mirrors.]

If they go through this much effort, there must be something valuable worth hiding. Whether it's a relic or some kind of information is another matter...though if the latter then we may be in trouble. Any books, unless somehow specially protected, will have long been destroyed by now.

Let's just hope whatever we do uncover is something that wasn't meant to stay covered.