Gylia Watch Tower Basement?

I don't know if this is for a quest or if it directly has to do with the ??? quest, but I found a hopper that does not seem to open anything when I throw an emerald into it. There is also a room/cave behind a bookshelf. The book in the bookshelf is called "Norler - The First Watcher". There is a small hole that allows you to see some type of room/cave behind. Again, I don't know if I'm being an idiot or whatever, but I found it interesting.

Here are the screenshots of the hopper below a gray carpet and the hole in the wall behind the bookshelf.

 

Library Key that opens the passage is found in the highest watchtower in the Gert camp. As for the hole, it's just a hole as far as I know.

 

A mage can teleport through the hole

 

This could be for "???". But we actually don't know because after you enter, you get teleported in a flat world and in the room is a bookshelf missing so some people say there is a second room. Unfortunately they don't know how to enter it because there are no hoppers or pressure plates in the first library.

 

Guys, did you tried to take the talking mushroom there (into the room that is missing a bookshelf)?

 

Thx. Never knew this place existed.

 

Actually didn't. I will try it tomorrow.