The Twilight Citadel is the great fortress city of the Twilight's Hammer, located southeast of Grim Batol in the Twilight Highlands. The citadel is a massive area surrounding a spire. At the summit of its spire is the entrance to the Bastion of Twilight. The structure, much like the majority of Twilight architecture is constructed from elementium. The massive spire of the Citadel can be seen from as far away as Thelsamar in Loch Modan.
The area was once the site of four Earthen Ring elemental portals similar to the Earthshrines, guarded by Earthcaller Yevaa. While the Ring was away helping to save Deepholm, the Twilight's Hammer moved in and corrupted the area. They then posted powerful ascendants to guard the portals.
In the TCG.