Old Minster, Winchester - Hidden Vault

Old Minster is an Anglo-Saxon cathedral built in 680 AD, and has a linked monastery. The current Bishop is Cyneberht, who resides nearby. The cathedral is part of the Winchester diocese, and part of the Wessex region. The nearest river is part of the Thames. Farmland, and a small town is situated nearby, providing services to Old Minster when needed. The monks are under the Order of St. Benedict.
Hidden within the church itself is an underground vault. The nave to get to this is in the west of the church, behind a locked oak door banded by black iron. The monks or the Bishop regularly have the key to this door. A set of cramped stone spiral staircase winds down to the vault itself, and takes the average person 5 to 10 minutes to walk down. At the bottom is a 15 metre long, 7 metre tall, and 4.5 metre wide tunnel made out of stone. Places on the wall are used to hold torches or candles. It ends in a stone door ringed by iron. There is a lock with a brass cover black iron cylinder number lock on it that is used to unlock the door. A seven number code is needed to be entered here to proceed. If entered incorrectly, it remains locked. 
If opened, the room beyond is the vault itself. The stone room of the vault is brightly polished, and cold. A candelabra stands in each corner, and the room itself is 20 metres wide, 20 metres long, and 10 metres high. A set of empty book cases run down the left & right walls, and the back has a false door carved into the stone wall.
On a dais in the middle of the room is a set of vellum pages and an open leather bound cover, with brass edges & corners. The pages are covered in Latin writing, and contains a spell to open a door to the 'Eternal Library of Life, Death, and All Knowledge'. If examined further, all the pages are stiff, and faded blood splotches are apparent. There are seven pages in total, and the inside of the book has some type of key to how the pages are to be placed. The leather of the book is also strange in appearance, with scars that are stitched together. If it is solved a being will appear to take away the summoner instantly.