Dushnikh Yal

Dushnikh Yal is an Orc Stronghold located in The Reach, southeast of Markath. Chief Burguk leads Dushnikh Yal and teaches Master-level One-Handed. When you approach the stronghold for the first time, unless you are an Orc, a guard will stop you and tell you that this place is exclusively for orcs and outsiders will not be permitted inside. However, if you ask her how she can be persuaded to give you access, she will tell you that you will have to reclaim an Item: the Forgemaster's fingers. This item can be collected in a randomized radiant location after a short quest. Return with The Forgemaster's Fingers and you're permitted to enter the stronghold. Give The Forgemaster's Fingers to Chief Burguk and he will name you Blood-kin of the Orcs and will offer Master-level training in one-handed.

Alternative Methods of Gaining Access
Head to Shor's Stone, a small mining town near Riften, where you will be given a quest to clear the mine of Frostbite Spiders. Once you have completed this task, speak to Grogmar gro-Burzag (an orc resident of the town). He will thank you for your help and tell you that you are welcome at the orc strongholds, and the orcs will not attack you. This opens a new line of dialogue: if you ask him about any "nearby orc strongholds", he will point you to one.

Another way is to head to Left Hand Mine, a short distance South-East of Markarth and speak to Pavo Attius and then clear Kolskeggr Mine of the Forsworn. Then speak to Pavo Attius again, and then to Gat gro-Shargarkh, who thanks you and tells you that you are welcome to the orc strongholds, and points you to one.

Yet another simpler way to gain the orcs to accept you is to talk with the Orc smith in Markath castle. He will ask you for a Daedra heart. Simply give one to him and you are named Orc-friend and can access the orcish strongholds.