Warsong Hold in Borean Tundra is the main Horde base in Northrend.

The base was built by the Warsong Offensive when the Horde landed in Northrend as a headquaters to house the army. The base also houses the leader of the Warsong Offensive, Garrosh Hellscream.
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Warsong Hold, Borean Tundra

The base also has a mine called Mightstone Quarry which has been ovenrun by the Undead Spiders called Nerub'ar.

There is a zeppelin Platform inside the fortress which goes to: