This is the base of operations of the ANBU Black Ops and the Tracker Ninja of Kumogakure. It is located just behind the gates of the village. This place has guards that watch over the gates, and any form of unauthorized exits of the village results in a guard being sent to follow the target; not to kill but to gain confirmation on their actions. The Headquarters also have a secret tunnel that leads to a room that's doors away from the Raikage's Office.
Here you can train and rest. ANBU and Tracker Ninja usually live here, with other ninja and village citizens using the headquarters as a hotel and a temporary living space in the Eastern and Southern Wings of the building.
The hallways of the administrative parts of the building are filled with ANBU masks, which represent the past members that might have resigned or have been killed. The first room in the building is the Head ANBU's Office which is also the first room you will pass by. This is where the ANBU meet to speak about missions that have been announced directly from the Hokage.
