I went to this at Donnington Park about 4 years ago and it was a real surprise. I had a great weekend, got thoroughly soaked but loved it. The Formula Renault 3.5s are just mental - take some ear defenders because those bad boys are seriously loud
Best bit for me is the F1 demo, I got to see Heikki Kovalainen ragging the hell out his motor when I went. Most impressive.
If you've got the time, go along
