An African tribe called the Ik throws their children out of their homes once they turn 3. They are left to fend for themselves with no help from their parents at all, and to survive, form groups with others their age. These groups only last a few years, and every so often the individual will join a completely different group.
One of the camels in the caravan trips over a dark rock protruding from the sandy dunes. The poor animal has broken its leg and cannot continue. A cacaphony ensues as the animal suffers and the caravan train overseers complain passionately as they redistribute the animal's load across the caravan. (Let's just hope none of the PC's was riding this camel, shall we?)
As the camel is put out of its misery and the camel is skewered over a campfire - waste nothing! - someone takes a minute to inspect the root cause of all the trouble. To their surprise, the upturned rock is worked stone. Some frantic digging may excavate the bottom half of a gorgeously worked1 obelisk, and maybe even the small square forum below; but a more rigorous exploration of the surrounding dunes reveals a buried tomb doorway on each side of the forum.