Exploring Hitler's Mountain (2006)

Adolf Hitler spent over 1,000 days on the Obersalzberg, his mountain holiday refuge near Berchtesgaden. It was there he made his decisions about war and destruction. The producers, through special permits, explore the abandoned concrete tunnels in search of the relics of history of Hitler’s mountain and to tell almost forgotten tales of the people who lived there, high up in the shadow of power.

Unfortunately the movie Exploring Hitler's Mountain is not yet available on HBO Max.