Kankoku Pass

As i understood it, for the coalition to take the capital of Kanyou they would need to take the natural fortress that is Kankoku Pass.

Why was everyone shocked including shin when he saw how big the Kankoku Pass is ?

Didn't shin go through it when he was in the capital for the award ceremony after Sanyou campaign ?

I am pretty sure that he went to the royal palace in the capital numerous times by now.