The most common and most likely answer to this crossword clue is the 8 plus 6 letter word TINTAGEL CASTLE
T
I
N
T
A
G
E
L
C
A
S
T
L
E
More clues leading to the result TINTAGEL CASTLE
Buddy explains!
The straight part
We know that "Cornish site" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cornish site = tintagel castle.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.