Basement

The basement (地下室) is found beneath the Yeager family's house in the Shiganshina District. This place was supposedly used by the head of the family Grisha Yeager for his work as a doctor; however, after the fall of Wall Maria, it was revealed that it actually stored an important secret concerning the Titans, and Grisha entrusted his son Eren Yeager with the key to unlock this secret and the mission to reach the basement and discover it.