Mazandaran
Where the road goes. Not the province on the map.
There is a real Mazandaran: the Caspian coast, forest and rain, one of the greenest parts of Iran. The Shahnameh's Mazandaran is not quite that place. It is somewhere behind a wall of mountains, thick with things that should not exist, and everyone in the poem understands that going there is a bad idea.
A king goes anyway, on a whim, because a singer describes it nicely. It ends the way you would expect, and that is what puts Rostam on the road. He is not opening up a frontier. He is going to fetch somebody who should have stayed home.
The seven stages are the crossing itself. Mazandaran is not a prize waiting at the end of them; it is the country they happen inside.
In the game
The road into it is the spine of the game. Where it ends is the game's to show you.