Ancient pages are items which are sometimes obtained when rummaging barbarian skeletons or as monster drops in the Ancient Cavern. Duplicate pages may still be obtained before completion of My notes if rummaging skeletons. They are part of the book My notes. There are 26 different pages. Finding all the notes is one of the requirements for the Trimmed Completionist cape and Master quest cape.
The door resists all of our efforts to penetrate it, even the Fishing explosives which Derril suggested were tried with no success. There must be some way through which is linked to magic though perhaps all who know the secret are now long dead.