Fort Neugrad

Fort Neugrad is one of the many forts in Skyrim controlled by the Imperial Guard.

In the quest Liberation of Skyrim the Dragonborn is given the task of gaining entrance to the fort (either by sneaking in, or barging in) and freeing a group of stormcloak prisoners.

It is occupied by a number of Imperials that shouldn't give you too much trouble as long as you aren't afraid to spill some blood.