During the grand campaign, you can only occupy the city of Karak Eight Peaks if you are the Dwarves, Greenskins or Elves. But to get this achievement you need to play as the Dwarves.
When you have occupied the city, you need to upgrade the main building to level 5. This can be achieved when you have enought growth in your region. After the city is upgraded to level 5, the achievement will unlock.