Imagine an hourglass, except rather than measuring hours, it counts out aeons. Its circumference is 40'000 Km (~25'000 mi). The glass walls are 100 Km (~60 mi) thick. The sand within forms a desert almost 13'000 Km (~8'000 mi) wide edge to edge.
The peoples within know not where they came from, or why, but all know where their end lies; the sinkhole in the centre of their world, 300 Km (~200 mi) wide and forever growing as the 1'000 Km (~600 mi) sandfall that encircles it erodes away the mountain-high perimeter. Even hundreds of Km away, dunes collapse seemingly for no reason as the sand shifts thousands of Km undersand. Some believe that it simply empties out in to space to become new stars. Others believe that it pours down over an entire other world like theirs. There is no way to know for sure, even if anybody could survive the sinkhole, there would be no conceivable way to return to tell the tale.
* * *
The whole herd clan are gathered to see you off. The wise woman of the clan places a wreath of cacti flowers around your neck and ritually kisses you on the cheeks and forehead. The riders steady the camel beside you, even though it is loaded down with more provisions than you have ever seen a camel carry, the beast shifts nervously, feeling the tension in the air. It has been painted with warding symbols for luck and dressed with charms and the people all touch it one last time for good luck.
The wise woman places her hands on your shoulders and addresses you calmly and clearly, "this camel has been trained from birth for one task only, she will head, without any need for guidance, toward the centre of the worldglass, to Journey's End, where all life drains away. She will refuse to backtrack or deviate too far, even if you beat her. The provisions you have will not be enough, she who carries you will return to the sands she came from and you will have to go the final leg alone. Spirits willing, you will be found by others before you too return to the sand.
"You must tell no other soul whomever where you came from. Nobody has ever returned from leaving but if you were to seek us out again, you would immediately be put to death. Our clan founder, the wayfarer, first and greatest of the wise women, warned us that for every wicked emotion there is a clan devoted to it, and they seek to find us so that they may take all that we have for themselves. There is greed and avarice out there, and selfishness, above all. Be on the watch at all times for where your clankind here welcomed you with open arms, out there you will be greeted with one arm open and one held behind the back, grasping a knife.
"Here, take this, the skull of my matron, the wise woman before me. Though we wise woman may never leave the clan, the wayfarer longed to see Journey's End with her own eyes once more and foretold that the spirits would call out to some among us to draw them to Journey's End, that they would grow restless and bring disharmony unless they went to their calling, even if only death awaited them.
"Now go, and do not look back, for you have been called and our love is the lightest load you will carry, may you take it with you all the way to Journey's End."