The most common and most likely answer to this crossword clue is the 8 letter word BALMORAL
I've seen this crossword clue in The Guardian
B
A
L
M
O
R
A
L
More clues leading to the result BALMORAL
- Party set up right in Scottish estate
- Black’s Tal? Ignore opening and just castle!
- Research establishment backed ethical cap
- Research place over upright castle
- Royal castle’s lip salve spoken of
- Said with relief where royalty goes in summer sometimes
- Raise little dog just for one’s holiday home?
- Petticoat causing guessing game in the course of dance
- Leading lady’s retreat just after party goes west
- Something soothing uttered in royal retreat
Buddy explains!

The straight part
We know that "castle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case castle = balmoral.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.
What does BALMORAL mean?
BALMORAL noun- A Scottish cap with a flat top and a plume but no brim; a blue bonnet.
- A heavy walking shoe.
- An Oxford shoe.
- A figured woollen petticoat.