Former Takizawa Honjin was a rest house that became a military headquarters during the Boshin War. It is closely tied to the Byakkotai story: the young fighters left from here before the Battle of Tonoguchihara and the tragedy later associated with Iimoriyama.
The building is a useful stop if you are following Aizu-Wakamatsu's samurai history rather than only visiting the castle. It gives the battlefield story a more human starting point.