On my way to school when I was a kid, I used to walk past the remains of a hill fort almost every day. the road was even called 'Castle Hill'. All that was visible was a small mound in a field, approx. 10m high and 30m in circumference.
I remember talking to the history teacher about it and remember being told that it was an interesting idea but there were no castles or forts in the area except for the one in the local big town, Barnstaple. What I could see was 'geology'.
Went right off history after that, probably because the teacher was a dumba$$.