Rereading again, after the webtoon was continued.
The Henkel Gate/Fortress is different than what I imagine based on the novel author description.
In the novel, Henkel Gate/Fortress is basically situated at a higher elevation than the surrounding area. Basically, it's near the peak of the two mountain tip, with winding roads to approach the gate through the mountain. While the Silence Imperial Side have an easy access and approach of the Fortress. With a Town/Village at the foot of the Mountain.