Almost every museum has a private warehousing facility, to hold items that don't fit in its public viewing space or perhaps to hold the originals of works that it doesn't want to risk to the hands of the masses. Jaguar, for instance, calls the secret overflow space it uses for its Heritage Center "Sleepy Hollow."
The $130 million Porsche Museum has 505 cars in its collection, but they aren't all on display at all times. That is why it has an exclusive location "somewhere in the surroundings and suburbs of Stuttgart" used for storage, as a staging area for cars headed to events, and as a vault for projects for other companies like Lada, Mercedes-Benz, Seat, and a concept for a family car for China.
The company gives us a look inside with the first two in the series of videos called Porsche Secrets. The first video is an overview of how the space is used, the second jumps into some of the special cars found therein, such as the 984 "Boxster Junior" concept from 1984 (in the foreground of the above photo), a 1976 924 concept meant to challenge the Mercedes-Benz C111 for endurance records, and a 906 Ollon Villars hillclimb racer. You can watch it below.