Explanation
You will see three rectangular holes in a room with five portals while navigating Level 7, according to GameWinners.com. Place any stone item in the holes, and you will receive three scrolls that help explain the game, according to the site.
Throne Room
You must complete the Special Quest for level 12 to find the throne room, according to GameWinners.com. Save the game before you fight Xanathar and complete the Special Quest after defeating him. The Throne Room will be revealed to you.
Glitches
Eye of the Beholder has a few glitches you can use to your advantage, according to GameWinners.com. Enemies cannot climb stairs or open doors, and you can block darts or arrows by closing a door in front of them. Entering the "camp" screen will allow you to see items behind doors.