Thanks, Bob and Pat, but what do you mean, personally?
To me, Brora has been a gem since I first played it in 1981, and it was "hidden" up until 2000 or so. I thought that Cruden Bay was a "gem" prior to playing it (although not "hidden"), but after playing it I have seen it as a very fine course, but not "gemlike" (per Arthur Pater--"...to burn always with that hard gemlike flame, that is success in life...."). Alternatively, after playing it, Cypress remains a gem even though not forevermore hidden.
I guess what I am getting at is that there are (to me--both experientially and vicariously) very few truly hidden gems. What think ye?