I used to visit the ROC bunkers mentioned above, there is also a restored Group HQ in York, which is open to the public if you're interested.
I haven't found anything of interest however the most facinating thing I heard about was on another forum of a guy in the US/Canada who was about 2 days from the nearest road, a gravel track rarely used at that. He had stopped to sort his pack out and noticed, propped against up a tree was a double barrel flintlock shotgun from the early 1800's. Loaded with lead shrapnel shot, with one barrel discharged and the other still cocked.
The buttstock desintegrated as soon as he touched it, all of the components were rusted and completely seized. He had already begun restoring it when he mentioned it.
Goodness knows how long that was sat there, untouched.