Pangaea, "Orbis Arcesso" is the name of the book that's used for casting the spell, along with the dragon scales (found in the room with the flying dragon, who is Amdusius--read his mind while you're in there talking to him), and a vial of Amdusias' blood, found on the table in his secret chamber-- where there is also a chest that requires a password. You'll have to read Amdusias' mind to find the password is "Lovis." There's dragon armor in there, and some other stuff, but I don't recall what. Each of the rooms on the upper level in the octogon (?) has a 'name plate' on the outside of the door to let you know to whom the room belongs. Amdusius' room as you stand in front to go in, has debris blocking walking around the 'balcony' to the right. Look at the bookshelf, and use it when the option comes up-- that reveals the hidden chamber, the chest w/ password (Lovis), and the vial of blood on the table (looks almost like a candle and I missed it on my second playing through!). As others have pointed out, you'll need to complete the Librarian's quest.
I usually went near the room where Amdusias is-- he's the dragon flying around. Read the book (which will be in your quest tab), which turns him into a human. You MUST defeat him in battle, and another book appears at the blood altar. Take that book, as it is somewhat vital to main quests through the end. When you do this, that barrier on that one door will be removed. You go into in, run into Damian (again), and have to fight a couple of his guys after the cinema. Go through the portal that is on that platform, and you're taken to Sentinel Island, which is also where the Battle Tower is located. You'll have many quests to complete there before getting your battle tower.
I hope this has helped make things clear to you. I want to emphasize again, you will have to defeat Amdusius before being able to proceed further in the main quest-- you cannot defeat Amdusius while he's in dragon form, therefore, you must read "Orobis Arcesso" while having the dragon scales & vial of his blood in your inventory. When he's human, fight & kill him (firewall & double-wield worked great against him for me).
Best wishes as you play the game. I'm playing through for the second time, and finding a couple of things I missed (minor things), which keeps it fun. I really do appreciate all the hard work that went into making this game-- it is challenging, but rewarding.
Best regards,
~~CierraShore
