Fenris Keep

The gloomy Fenris Keep lays at the center of Lordamere Lake in Silverpine Forest upon the Fenris Isle. The keep had strategic significance, and was home to a sizable portion of Lordaeron's military. During the Fourth War, after the Battle for Lordaeron, it was contested between the Alliance and the Horde, but the Bloodfang Pack managed to reclaim it from the Forsaken.

Third War
When the undead Scourge washed over Lordaeron, Fenris Keep was not spared. Thule Ravenclaw, an ambitious young mage formerly of the Kirin Tor, allied with the Scourge, and dominated over the local gnolls, creating the Rot Hide. He made himself master of the keep.

World of Warcraft
Thule Ravenclaw commanded a large force of Rot Hide gnolls to do his bidding, which hungrily attacked anyone who neared the keep and their master. As such, they were often targeted by the Horde adventurers. They were eventually driven out of the keep by the worgen.

Cataclysm
After the fall of the Southshore and Hillsbrad Fields towns to the Forsaken at the command of Sylvanas Windrunner, its refugees, including their leader Magistrate Henry Maleb escaped towards Silverpine Forest and occupied the keep as their base of operations. When agents of the Forsaken, along with Agatha, entered Fenris Keep to kill the Refugee Leadership, they were met with a surprise.

The worgen leaders Darius Crowley, Ivar Bloodfang, and some of their forces attempted to convince the humans to drink their blood in order to prevent the refugees from becoming part of the Forsaken, rendering them immune to undeath, as well as assist them in retaking Lordaeron for the Alliance. The refugees decided on the lesser of the two evils and drank Darius' blood, becoming worgen and temporarily driving the Horde away. Several hundred Hillsbrad Refugees became Hillsbrad Worgen shortly afterwards, with Ivar and the others having apparently made their blood offering to every surviving human in Lordaeron, and openly fought with Forsaken forces in Silverpine Forest.

Battle for Azeroth
By the time of the Fourth War, the Forsaken forces led by Deathstalker Hayward captured Fenris Keep. Alliance champions were sent to annihilate the undead to secure Lordamere Lake, with the Bloodfang worgen eventually re-taking the control of the isle. This forced the Horde to create a distraction along the Misty Shore to lure the worgen out of position, allowing Horde refugees to escape Tirisfal Glades across the water.

Exploring Azeroth
Mathias Shaw noted his main contact in Silverpine Forest as Ivar Bloodfang, stating that the packleader was his contact within Shadowfang Keep. The pack has apparently claimed it, along with maintaining their control over Fenris Isle, and have taken most of the artifacts within Shadowfang Keep to Fenris Keep to be guarded closely.

In the RPG
Lordamere Lake contains an island called Fenris Isle. This island once held a great fortress known as Fenris Keep, but the structure has sunk into the bog and is now mostly submerged and covered with mud and scum. If you want to kill murlocs or Rothide gnolls, this is a great place to do it.