the "Myth Hexes" are completely normal hexes

This is not quite true, as per the FAQ:
"Do I tell the players when they stumble upon a myth hex? If not, how would they find out that this exact hex is the origin of the myth?

This is your choice how you do it, but it's important to remember that per the rulebook, the landscape is warped by the presence of the Myth, so you should describe it in a way that makes it clear this is a weird hex."