Not long ago, they found a car they'd completely forgotten about - a Porsche 924 made entirely of body filler. Not really, but that's what it looks like. Equipped with a 250-litre fuel tank, lightweight panels, a massive turbo and a primitive low-drag body it was intended to break speed and distance records, but Mercedes did something similar first, so Porsche hid this curiosity under an old blanket, behind a huge crate. And forgot about it.

There are other one-offs, too. The prototype 965, designed to fit between the 911 and the 959. That never saw the light of day. Nor the unique V8 engine inside it. There's a 968 Club Sport Cabrio, a ragtop 928, a latticework concept designed to test longevity (don't ask me how) and the Studie C88.

This last isn't really a Porsche at all, but the result of a competition the Chinese government held to design a car. "It only has one child seat because of the country's policy on children", Landenberger tells me, "and when we presented it, Dr Weideking [former CEO] learned his speech in Mandarin. But at the end it didn't help. The Chinese government said thank you very much and took the ideas for free, and if you look at Chinese cars now, you can see many details of our C88 in them."

There's some lovely personal stuff, too. The Porsche family order all their cars in the same forest-green shade, because it links to their love of hunting. There's the first ever 911 Turbo. It's unbadged with sports tartan trim down the flanks and was a birthday present for Louise Piëch (Ferdinand Porsche's daughter) in 1974.

Speaking of the Turbo, there's even a disguised version of the forthcoming 991 Turbo parked down the quiet end of the warehouse. I give it the once over, my eyes coming to rest on the keys left somewhat carelessly on the dash. World exclusive drive in the next Porsche Turbo, anyone?

I'd tell you to come here, but you wouldn't be allowed. Porsche is keeping this place secret. That's a great shame as these cars are as interesting as anything you'll see in the museum; they're just surrounded by slightly inferior architecture.

That will change, though, as Porsche intends to cycle these cars out to the museum, overseas shows, even rallies and races. And yes, even the one with the ski-binding boot clip.

This feature first appeared in the October 2012 issue of Top Gear magazine