Chronicles of Bilrach
The Chronicles of Bilrach are journal pages found during Dungeoneering which can be read (and later re-read by talking to the Dungeoneering tutor). The various entries were written by Bilrach, a Mahjarrat, detailing his travels through the dungeons of Daemonheim in search of a portal he calls "The Rift". This rift would, in theory, release the Mahjarrat god Zamorak from whatever realm Guthix banished him to after the God Wars, resulting in Zamorak rewarding Bilrach in one way or another.
Every mysterious chronicle has a 1/4 chance of spawning at the end of a Dungeoneering floor.