The Iron Sea

The Iron Sea was the region in which the Dwarves lived in three giant underground cities known as Dwarfholds.
During the Shatterwar the Dwafholds of Egregor and Zarafheim were destroyed by subterranean horrors sent by Delvash in order to keep the Dwarves out of the war.
[Paragraph on how the other Dwarfhold was lost]
Following this, the Dwarves moved into the former Ytarran nation of Ytarra, renaming it Tarq.
== In other planes ==
The Shadowfel equivalent of the Iron Sea is known as The Cauldron and is filled with incredibly powerful spirit shackles. Alyssa is constantly trying to seize it from Hastings, and it is said to be the only thing making him powerful enough to keep her and Lockhart from taking him out entirely.