Heimlyn Keep is located on the southern roads in Zabamat that lead into Varanis & the Iliath Temple to the west and Lukiul Uxith to the north. Heimlyn serves as a fortress to the Great House Telvanni, and because of this, Heimlyn is heavily fortified, and it looks over northern Stonefalls. It has only one entrance in the north, and upon entering, you are greeted with the town square and surrounding homes. Advancing more inward is the inner temple that leads to the Reliquary.
During the Interregnum in 2E 582, the Ebonheart Pact waged war with the Daggerfall Covenant in the Stonefalls region of Morrowind. The Covenant was able to besiege the city of Davon's Watch and was able to conquer Bleakrock Isle in the Sea of Ghosts. The Covenant raided various settlements throughout Zabamat, and this included Heimlyn Keep. The Keep was under the control of House Telvanni, who was neutral in the Alliance War and did not associate with the Ebonheart Pact, whatsoever. The Covenant was not aware of this and attacked Heimlyn Keep with ferocity. This triggered a defense mechanism created by the Chimer and ancient spirits drove away from the Covenant and took control of Heimlyn Keep and its citizens.[OOG 1]
A mysterious traveler that was known as the Vestige arrived into Heimlyn Keep and was asked by Beron Telvanni to help Heimlyn Keep and to disable the reliquary. The Vestige traversed the Keep and disabled the Daedric Ruins set forth by the Chimer. With the help of Keeper Vildras, the Vestige entered the reliquary and defeated the spirit guarding the inner sanctum. The battle to beat the Daggerfall Covenant moved northwards in Fort Virak where General Serien and his army is stationed.
During the Imperial Simulacrum in 3E 399, the Heimlyn Keep township existed in Morrowind in between the towns of Narsis and Oaktown. At one point, the Eternal Champion had visited the city in their quest for a piece of the Staff of Chaos to defeat Jagar Tharn at the Imperial Palace.