Neue Wache
According to Wikipedia: "Dating from 1816, the Neue Wache was designed by the architect Karl Friedrich Schinkel and is a leading example of German neoclassicism. Originally built as a guardhouse for the troops of the Crown Prince of Prussia, the building has been used as a war memorial since 1931." Today it houses a memorial to victims of Fascism. We didn't know this at the time so we just passed by and took pictures of this cool old building.