Its officially classed as a one-way unrestricted public toll-road. Hence why, legally, insurance companies MUST provide you with third party insurance cover whilst on the 'Ring.
That's what the people who want to drive it and be insured say but the insurance companies have another view. It was purpose built as a racetrack (by Hitler incidentally), it doesn't go anywhere, it isn't owned or maintained by any road authority and you are only ever on it for fun.
The official figure is 73 corners but they only count areas with coloured kerb stones, don't count little kinks or twists and a complex of bends would count as a single corner. I think the driving enthusiasts version of the total is around 137 ish.
It is ALL a racetrack and that's what it was built as. It is one long circuit that can be seperated into many smaller ones like most circuits can. Originally it was the north circuit (Nordschleife) and south circuit (Sudschleife) but the south circuit is all but gone now. Actually the road that the campsite is on is part of the original south circuit and that may be why it is quite a fun road. The current FIA circuit at the 'Ring replaces the south circuit but only actually uses a very small part of the original route and is a lot shorter than the original. The FIA track can still be joined to the north circuit to make one big track though.