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.
Our theory of artificial origins has been vindicated! We have discovered a sturdy door, which seems to be a similar age to the original excavations. I am sure that there is a magical or mechanical activity behind it, though it may be simply be a great rush of water.