yes, been many a times before. its free to watch track days and practice days on events such as super bikes, touring cars etc
theres a barrier but they let you though, of course you cant get on track with out a pass any way so they know theres no chance of you sneeking in, you drive down behind the grand stands then past the paddock shop. then do a sharp right then go under the track though a tunnel, (which is awsome for sound btw lol) then you appear up behind the garages/paddocks so your on the fences of cooper straight between graham hill and surtees.
but last time i was there on a track day, as long as the pits are free of cars, and your over 18, you can stand on the pit wall and belive me when theres some big turbo'd cars going full speed full throttle past there its quite amazing! and back to cooper straight its cool to see people passing etc up to surtees and up round mclaren corner