I never ended up running this, but it could be an interesting treasure hunt game or two. The premise is that the party encounters a Xaositect who gives them the following rambling clue (to find something truly lost):
O hidden sun, betwixt Aether and Flame,
O black sun, light of mortals' shame,
O scarlet sun, the perfect name,
From the three, the Stone first came
The Alkahest, the fountainhead,
From whence the power to raise the dead,
And form pure Gold from tainted lead,
Its secret long since gone unsaid
A name writ once in fire and ice,
Stolen by a thief precise,
Who lost it in a game of dice,
On a bet for his soul - a trivial price
The victor wrest it from his grip,
The sweetest wine was his to sip,
He left upon his skeletal ship,
To chain-ed realms the damned call kip
With glowing eyes and snarling face,
He fell into the stone's embrace,
And into Gold did turn his race,
A shining palace in thrice-bound space
Deep within the terror's howls,
Deep within the prison's bowels,
With twisted figures' frozen scowls,
The secret rests and waits... and prowls.
What this means:
The philosopher's stone is made from the combination of the black sun and the bright sun, but also requires distancing from the two. If one goes to the points equidistant from the resting places of these two objects, one of them might contain the philosopher's stone.
The black sun exists upon Athas, and is the Dark Lens created by Rajaat, the first sorceror. Through the Dark Lens, Life can be transmuted into magic.
The hidden sun exists upon the Ethereal plane on the border to the plane of Fire. It is a spot where the Fire is being channeled into the plane of Fire out of a rift in the Ethereal.
The scarlet star is a ruby within which are stored the echoes of the words spoken when the multiverse came into existance. The scarlet star is currently part of the Wand of Orcus.
Acquiring the three origins of the stone is nigh-impossible, however. More realistic is following up the second part of the riddle. The secret of the stone had been taken by a creature belonging to a race of demons that no longer exists to one of the orbs of Carceri, where it is entombed within a palace that shines with an inner light. The palace is thrice-bound - this means that it is on the fourth layer of the sphere it is on - and is guarded by the statues of the race that the Stone destroyed. The Stone itself has a tangible presence, and wanders the halls of the palace.