Well unfortunately I'm on the same problem as I've just finished reading the setting and I plan to run a similar campaign(to start on Anias and end up in Belynar), so I got nothing. But I'm thinking since it's a key mountain pass it should have some sort of fortress to defend it, maybe a merchant town or even an old abandoned Empire outpost, IIRC that was the frontier of the former Empire, so there should've been some defensive system on that side of the mountain. That said castle/town might not be inhabited anymore but other creatures could've taken residence. Or maybe the Orsai went around the mountains by sea to seige Tarahir from every side, that would explain why Grayson and the others had to escape through the Dwarven outposts and not to the east through the mountains, the characters could be the first to find the Orsai sneaking troops through the mountain and now have to find a way to get past them to alert the Tarahiri.
You can put just about anything in the form of ruins, since it's the NE part of the former Tarahiri Empire border. Haunted places, abandoned outpost, mountain creatures, ruins that tell the story of the past, or they can even spot the Dwarven outpost(dangerous idea if the Royal Roads are already active) so they are the ones who tell Grayson they can find cover that way. Depending on the timeline you can add flavour by adding the towns on fire, the refugees fleeing to the city, burning fields, maybe a wizard being hunted or burned in the pyre, Gryx getting killed, and you add the challenge to sneak behind the enemy lines.
Not the greatest ideas in the world I know, but that's what I got for now.
As soon I start to prep my own campaign I'll share some specifics, but right now I'm just gathering seeds of ideas.