Harrowsdeep

Harrowsdeep was the home of Iridikron 20,000 years ago, during and prior to the War of the Scaleborn. After Iridikron usurped control of the Primalists from Fyrakk, Harrowsdeep became the faction's center of power. The tunnels were dug out by Iridikron. Located beneath a towering mountain north of Dragonblight, the entrance to Harrowsdeep was a cave mouth at the base of the mountain encrusted in ice and snow. A massive sinkhole in the center of the entrance chamber leads to a pool of water at the bottom, with a waterfall coming down the hole. From there, dark tunnels led further underground. Iridikron's war cavern within Harrowsdeep was a massive, dark chamber with a lake of magma and several islands of stone, as well as a central platform where Iridikron conducted his business.

It may be the same place as Naz'anak: The Forgotten Depths, which is also located north of Dragonblight and looks similar to the description of the entrance hall given in War of the Scaleborn.