The Tower of Ninjas is the home of the Black Dragon Ninjas. It is located in the northeast region of the Border Zone. This location can be discovered by reading a Tech Hunters Map.
Upon entering the tower, the Black Dragon Ninja faction becomes hostile and attacks; they will, however, also attack mobs like Dust Bandits, so you can lead a group in to help. The layout of the tower is very similar to that of a Shinobi Thieves tower, with Black Dragon Genin manning four crossbow turrets on the roof.