Illidari'Aran is the name given by Demon Hunters to the subterranean labyrinth of tunnels, Barrow Dens and caves that traverse beneath Felwood in northern Kalimdor. The tunnel network in its entirety is a sprawling and disorganized system of abandoned Barrow Dens, natural caves and carved tunnels that run underneath the slopes of mount Hyjal. Most portions of the cavernous realm are ancient Barrow Dens, either abandoned by druids or taken by force from the Shadow Council. Other portions of the cave network are recent additions carved out by demonic labor, expanding the underground network, while other portions of Illidari'Aran are vast, natural caverns with geological features from underground lakes to nests of indigenous creatures.
The vast system of tunnels and caverns is by no means an organized or even connected region. Due to their age and lack of maintenance, several passages have collapsed, sealing away portions of the tunnels for centuries only to eventually wear away a new entrance. Traps litter the abandoned halls as well, with both mundane mechanical triggers and more complicated and equally malevolent magical wards. Several tunnels connect to the Shadow Council stronghold of Shadow Hold, though few have ever managed to find them without becoming hopelessly lost.
At the heart of this disorganized maze of caverns lie the Halls of the Illidari. Here, Demon hunters gather to recuperate between hunts, resupply, and develop the spells and techniques necessary to continue their eternal war against the Burning Legion. The central chambers are home to trophies of the Hunt as well as relics of past glories. Tattered banners of the Illidari recovered from the Black Temple hang from the high ceiling, some still coated with spatterings of blood. Demonic skulls and sundered weapons line the walls in bold declaration of their defiance against the Burning Crusade. Those few beyond the Demon Hunters who manage to avoid the multiple traps, guards and wards necessary to find this sanctum often awaken in Ashenvale forest with no memory of how they got there, but the bold and persistent may yet find their way into the halls.