[@Haeo] No, it is not a location from the game. It had been occupied by the Forsworn since the Markarth Incident. The redoubt itself is on top of an abandoned mining camp, it known as Neckbreak Hill on certain maps, and it is defended by palisades 3 to 4 meters (12 feet) tall. Both the merc camp and the redoubt are on bluffs with a 20 meter (21 yard) deep, and 2.5 kilometers wide (1.5 miles) valley in between. The valley has a small of creek running through it, the creek water is waist-high at the deepest, and has a ford big enough for carriages to pass. Neckbreak Hill has a mining tunnel underneath, it doesn't lead inside the redoubt but opens to its rear gate. 

For the last decade, no one has been able to get inside the walls. However, scouts have been within five meters of the palisade. The main road and several side paths are bobby-trapped with tripwires, warning bells and spike pits. Daelin managed two recon missions before he stopped going so close, reason being that these two missions costed four lives.

Both the merc camp and the redoubt are not directly beside the road. They are both 3 kilometers (2 miles) from the road, a small mountain separates the camps and the road. The valley and the foothills are dense with bushes, which are easy to get lost in. 

And no, the redoubt is not visible from the main road. But it is close enough to launch raids.

Made some crude maps for reference. They're not drawn to scale and drawn on track pads (cut me some slack, ok?).

Location in the Reach.

[img]http://s17.postimg.org/pm3mtvc0v/mapppp.png[/img]

And local map.

[img]http://s11.postimg.org/6xlgjxuur/mapppppp.png[/img]