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.
I must caution against offering the wrong gifts to the spirits inhabiting the world beyond this. They seem quick to anger if the offerer was in any way responsible for the offering's death.