Interesting documentary about a group working deep beneath modern Berlin to discover and preserve complex tunnels of bunkers, even as the city is destroyed. Here’s the official program description from National Geographic Channel:
Hitler’s Hidden City is a subterranean adventure under the streets of Berlin, following the work of a team of German archaeologists and historians exposing and exploring the last remaining structures of the Third Reich. We gain rare access to an underground city ordered and — in part — designed by Hitler himself, part of a vast network of over 1000 bunkers and many miles of tunnels, much of which has remained sealed since the war. Eyewitnesses and historians add colorful stories to cutting edge CGI that bring to life this network of bunkers, how they were built and how they were used in the dark days of the downfall of Berlin.