Ninja House (STW building)
The Ninja House allows you to produce Assassins trained in the art of Ninjitsu. They can be used to kill important individuals such as Generals and Emissaries.
The secretive ninja require their own dojo (of sorts) to learn their black arts of assassination and spying. Their weapons and skills are so specialised that only a master ninja can hope to teach his followers, and even then it may take many years of training starting in childhood to produce one of these lethal killing machines.
Once a fortress has been built, an Infamous Ninja House can be constructed.