The dread Tower of Inversion, lair of the vile lich Zarakoth Xorast, contains five layers, each containing different tools of dark magic.
Over three hundred years after the destruction of Linnarson, the ruins of Linnarson remain deserted; the warped magical environs inhabited only by the twisted and bizarre creatures that have been created. Amongst it all, however, the Senior Masters remain, continuing their eternal pursuit of knowledge. (UPDATE IN PROGRESS.)
Maranesh, God of Magic, wearied of the multitudes of humans who came to him, clamouring to be taught the secrets of magic. So it was that he devised a test that would separate the worthy from the unworthy.
You have all chosen to follow the Path of the Philosopher. Not for you the warrior Path of the Battlemage, fighter for justice, nor the Path of the Healer, worthy though it may be to heal the sick. Equally you have rejected the Path of the Artificer, the tinkerers, who work on devices and techniques, as well as the Path of the Loremaster, who merely delves and catalogues the knowledge of the past. No, you have decided upon the Path of the Philosopher, the highest calling, the way of true enquiry, where you will probe the realms of higher mathematics, ponder the meaning of truth itself and tease out the deepest secrets of nature and the workings of the world.
If you want to add a "supernatural" touch to your campaign, define the rules of magic and the universe. Make your players comfortable with those rules. Then your new supernatural creatures must then break those rules.