The oldest mystery in Human mythology is the end of the Epic of Etana. A wise king, desperate to provide his people an heir to stave off the chaos to come. In the real world, we know he succeeded. But we don't know how. MayD and I have provided an answer, though perhaps not one that does justice to Etana himself.
The translations presented here are heavily modified versions of real translations of the Sumerian King's list and the steles we have about the Epic of Etana. Even Sargon's boasts are about 50% true to a contemporary text, though I'm hardly the first to re-purpose that apocryphal tale (glances at story of Moses).
There's some crosslinks in here, though the text color of the Css makes them a bit hard to spot at first glance.