Donitz’s command bunker today
When the Allied bombing campaign of Germany began in earnest, B-17s by day and Lancasters by night, the Kreigsmarine went underground. U-boat papa Karl Dönitz set up a command bunker (Führungszentrum des Oberkommandos der Kriegsmarine) under his more pedestrian above ground headquarters in the woods outside of Berlin codenamed Lager Koralle. There, from 30 Jan 1943 till 20 April 1945, the Befehlshaber der U-Boote (BdU) directed the operations of Germany’s sub fleet and surface raiders alike.
With the Soviets pushing in from the East, Dönitz moved the command itself to “Objekt Forelle” in Plön, near Denmark, where he directed the last act of the German war effort. In the process, the Germans burned the documents they didn’t take with them, and smashed or blew up what they couldn’t.
Then the Soviets moved in after and leveled the surface but overhauled the subterranean bunkers, using it as a special munitions storage site until 1989 when they pulled out for good.
Now Lager Koralle, fully abandoned for nearly four decades, remains as witnessed by the below recent video from Crazy Places, released in February.