Inspired from the former posts, and by the biblical tower of Babel, my idea would be:
that maybe from outset the possible motivation for the PC's magi might be something less than magical power - maybe an seemingly simple challenge: the magi have somehow acquired an interesting text. Though that text might certainly be believed to harbor great magic...
Maybe its ancient, maybe it's a more recent copy of an old text, but the important part being that it is written in a language that the magi don't know. They might realise, as they try seek out other learned people, magi or not, that it really is an unknown/forgotton language. Yet even the parchement itself or the inks seethes with power. Power and mysteries beckon to every sane (and insane 
) magi, the unlocked secrets being a constant thorn in the side of the magi.
Now, what if during the PC's research/role play (using many of the brilliant ideas above) the finally stumble on or find a wise man (use any appropriate archetype that suit you) that reminds them of the fable of Babel - that if they seek to unlock mysteries in a forgotten language, then the only way might to seek the ruins of Babel (all languages being one).
Now the board is set and you (and the PC's) can move the pieces... There might be room for an interesting sub-adventure as they travel toward their destination. There might be interesting portrayals of the local culture and related plots, hermetic and mundane. There might be intrigueing amongst the members af the travelling party: magus vs. Templars, Magus/Templars vs. superstitious grogs, Templars vs. Templars (godfearing vs. corrupted). The last one might even inspire an "Orient Express" story (isolated in the deserts/mountains in a small travelling party mysterious deaths starts happening, becomming more and more incredible - maybe the corrupted Templars working to "clean" out their loyal counterparts? Maybe some of the grogs are more than meets the eye? Maybe the magus is under suspicion? Which might lead to the magus feeling stressed that if he do not reveal the real culprit(s) he might suffer...)
Finally they find their destination and one can do what ever one feels like. Searching and "dungeonering" or simply tell the unweiling of the underground cave and then whatever happens there. Maybe a climatic resolution of the "Orient Express" and the intergroup intrigues.
But what if there remains a final coupe de grace..?
That when the magus finally gets to translate the ancient parchment - using magic found in the cave, a mundane translation key or doing a "Rosseta Stone" (finding a tablet or insciption with the same text as on the magus' parchments, except that the same texts is also inscribed in another known language - maybe greek or hebrew - or in the spirit of the fable of Babel, maybe it's an enormous inscription saying the same in every existing written language, covering an entire cave or even a foundation wall remaining from the Tower) - that the texts is actually a strong warning to never disturb the resting place of the twin fiends! The warning might be mundane or divine, whatever suits your saga.
Thus the morbid irony is that the text that where to warn mankind to ever disturb... becomes the very reason "something something" (evil? the punishment of God?) being unleashed once more on the world! Now that's a fiendish plot, indeed...!
Off course being very keen on handouts myself to fuel the imagination of my players, I would create a mysterious enticing parchment to lure the unsuspecting players.... I actually did something alike it - 2 years (real time!) back I introduced something like it. An undecipherable text, that for now rests with the covenant as a foreshadowing of a interesting and strange story yet to unfold...
A digital copy of this handout is of course available to my SG sodales, if you just send me a personal note with your e-mail, I'll mail it (in Word or probably Acrobat Adobe).
), trapped by one of the Elder Gods....