Sometimes, there are things you just can't do on public roads.
Above is a little video tour of the Millbrook Proving Grounds in the UK, via Autocar and a Jaguar XFR. You've probably sen this track on Top Gear, Fifth Gear, and just about every other British auto publication ever made. You can see their banked oval, their mile straight, their tiny narrow road course, and their absolutely wonderful hill route. It's a perfect country backroad, complete with lane dividers, only completely private and open for use.
It finds its way into my dreams some nights.
What do you think is the most amazing, incredible, secret, wonderful test track or proving grounds in the automotive world?