'Das Architektonische Lehrbuch' by Karl Friedrich Schinkel (1979). Publication of the unfinished book on architecture Karl Friedrich Schinkel worked on during a large part of his professional life. His work never fails to amaze and inspire me.
Close up of the famous 'Lange Blatt' with preparatory sketches by Karl Friedrich Schinkel for his 'Architektonische Lehrbuch', showing the historical development of making spans in architecture. Very inspiring.