Wrangel Island is an island in the Arctic Ocean, situated to the north of Russia. Wrangel Island is the seat or the base, of all of the wards that protect the world, and Idris in particular, from demonic invasions.
In 2007, the wards over the island were smashed through; though the Clave did not know how it happened, they decided to prioritize fixing the wardings over Wrangel Island rather than focus on the ongoing search for Jace and Sebastian. Unbeknownst to them, Sebastian opened a gate with the intention of luring Greater Demons into the world through it with the promise of making them the patron of the Infernal Cup, though in reality, the Cup would destroy them. Breaking the wards also helped him in his summoning of the still-scattered Lilith, who eventually donated her own blood that made the Infernal Cup demonically-aligned.
In preparation for the impending war, the Clave sent several experts to the island to help strengthen and reinforce the wards, particularly those over Idris and Alicante, where the Shadowhunters were all staying until they could formulate a strategy against Sebastian and his Endarkened army. After the war, Helen Blackthorn, a Shadowhunter who was also half-faerie, was stationed at Wrangel Island to study the wards, even though the norm for Shadowhunters over eighteen was a mere posting to a different Institute. While the posting may have been considered an honor in other circumstances, in this case, it served more as a punishment, a sort of exile from Helen's home in Idris and Los Angeles, due to the fact that many Nephilim were suspicious of all Fair Folk after their unexpected betrayal.