Manaforge

A manaforge is a structure that harvests mana from the Twisting Nether. Manaforges suck energy from Nether (same energy that mages use at their spells) ands its used by Kael'thas Sunstrider to create Sun Gates. Their original purpose is unclear, though their architectural similarity to Tempest Keep implies that they are of naaru manufacture, much like the Keep itself. So we can speculate that when Kael'thas armies took Tempest Keep from Naaru they also took Manaforges.( Execept Manaforge Ultris that is taken by Voidwalkers, likely before Kael'thas. Reason that Kael'thas has not tried to capture it too was maybe that they are in same side.

Five manaforges are operating in the Netherstorm, under the control of blood elves loyal to Kael'thas Sunstrider. They are: