What it says on the tin.
During the war, there were constant rumors that the Reich had begun construction of a final redoubt in the Alps, where they and the remnants of the Wehrmacht would hold out against the combined allied forces.
Ultimately, this all turned out to be a complete fabrication designed as a smokescreen to distract the WAllies, and Hitler never approved the plan. However, what would it take to get the Alpine redoubt actually constructed? How would it aftfect the Aliies strategy?