The Black Temple is the fortress-citadel of Illidan Stormrage, Lord of Outland. It was once known as the Temple of Karabor, and has changed hands many times over the generations
It is a level 70 raid instance in Outland, containing tier 6 drops and the Twin Blades of Azzinoth. The entrance to the Black Temple does not appear to be its main gates, but rather an instance portal set in a breach in the southern battlement, below the ruins of Karabor. It no longer has a required attunement.