For this achievement you'll need to build the Dark Crag building in the city of Hag Graef. This can be obtained in both the Eye of the Vortex campaign and the Mortal Empires campaign.
In both campaigns it's part of The Black Flood region as part of Naggaroth.
Occupy and upgrade it to a lvl 4 city and build the Face of Hag Graef. Upgrade the building to The Dark Crag and the achievement should unlock.