Never heard about it...until now.
Here is a
link with a picture gallery how it looks there now.
I found also a forum with a discusion about it...unfortunately in german...
Those two photos are taken of that forum. Copyright???
This is the link to that tread It seems that all started of with 'Alt-Auto-Rennen' (junk-car-racing?) called 'Auto-Speedway' on a incomplete track. Then it envolved:
Link to a gallery from 1984And came to an end in the mid-80ies...supposedly because of residual pollution. The people that live around there on the other hand were or still are known to bitch about every little noise on their holy sunday afternoon...
That is basically what I found out.
Hope that helps a little.