Whilst out and about I came across this:
http://www.bristolmountainbikeclub.com/gallery/_2006/06_03_27_MTB_Misc_MP/images/IMG_6665_JPG.jpg
It's a ROC Nuclear Observation Bunker at Hallen, Bristol. I've only started noticing this stuff after watching the recent channel 4 programme "Real Dads Army" about bunkers, stops lines etc. There popping up everywhere.
It only closed in 1991, I cant believe I passed this site nearly everyday and never noticed and realised all those RAF types scurrying around underground, scary. Looks like Avonmouth was the only interest at the time, not Bristol :-(
Check out this site which has a cut away diagram:
http://www.subbrit.org.uk/rsg/roc/history.html
Anybody else noticed sites like these near other ancient site. Looks like man has always had a thing for hills, be it Hills Forts to modern bunkers ;-)