The most common and most likely answer to this crossword clue is the 11 letter word STRONGHOLDS
I've seen this crossword clue in The Guardian
S
T
R
O
N
G
H
O
L
D
S
Buddy explains!

The straight part
We know that "Keeps" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case keeps = strongholds.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 STRONGHOLDS mean?
STRONGHOLDS noun- A place built to withstand attack; a fortress.
- A place of domination by, or refuge or survival of, a particular group or idea.