The Discovery of the Boundless Lake

The Discovery of the Boundless Lake is the prophecy foretold by the Rain Priests which tells of a stray wanderer discovering a great expanse of water, that has no visible limit, and coming back as a hero to the people of Veyetræll.

Summary

The prophecy says the hero is of uncertain origins, but that they have heaps of courage to spare.
Supposedly fleeing persecution and a certain death, the hero decides to leave Veyetræll against the will of the Gods. They manage to go through the Veracious Pass and leave, going north and following the river. 
They face many dangers, including mythical beasts and unforeseen celestial events, but come across hints of the existence of great amounts of water at the end of the river. The Sel Dam is mentioned in the histories as an immense structure foretelling the expanse.
Eventually they come to what is called "The Ocean", a boundless surface of turbulent water with waves much bigger than those of the lake around the Isle of Sylgadrig.
They bring back riches the Valley has never seen, and are hailed as a hero by their former enemies.

Spread

The myth has spread across Veyetraell since the The Invasion and the spread of writing.

Cultural Reception

It is common for one child in the family, often the black sheep, to see themselves as the foretold hero and slip away in search of the Ocean.
Now, the Veracious Pass is heavily guarded and frequently turns in those marauders. But some slip away, and all have yet to return.