Book of the Ancients
Wondrous Item, very rare
This magical, leather-bound tome is thick, heavy, and covered in runes. It is always dusty, and it looks and smells like it has lain undisturbed in a library for millenia. The first page has a signature from the Owner. If the Owner dies, the signature disappears and the entire book becomes blank except for the first page which has the words "This Book Belongs To:" with a blank line beneath it. The next person to sign the book becomes its Owner. While the book is Owned, no other creature may sign the first page.
This book may be used as a spellbook. It has infinite pages and is immune to damage from non-magical sources. If you become this book's Owner, all Wizard spells you know are instantly copied into the book for free.
While you Own the book, you always know its location relative to you unless it is on another plane of existence, in which case you know on which plane it is located.
While you Own the book, a creature other than you that reads it finds it to be complete jibberish regardless of languages known or magic influence. After each minute that a creature reads it, it must succeed on a DC 14 Intelligence saving throw or become stunned for 1d4+1 hours.
Each time you gain a Wizard level while you Own the book, you can add one additional Wizard spell of your choice to this spellbook for free. This spell must be of a level for which you have spell slots, as shown on the Wizard table.
When you cast a spell that requires Concentration while you Own the book, you can concentrate on up to two different spells at once without breaking Concentration. If you cast a third spell that requires Concentration or if your Concentration is broken for any other reason while concentrating on two spells, it is broken for both spells. After you use this ability, you can't use it again until you complete a short or long rest.
When you are attacked or take damage while you Own the book, you may use your reaction to cast a spell with a casting time of 1 action. After you use this ability, you can't use it again until you complete a short or long rest.