Strongholds in castle I’d converted (8)
I believe the answer is:
citadels
'strongholds' is the definition.
(citadel is a kind of stronghold)
'castle i'd converted' is the wordplay.
'converted' indicates an anagram.
'castle'+'id'='castleid'
'castleid' anagrammed gives 'CITADELS'.
'in' acts as a link.
(Other definitions for citadels that I've seen before include "Keeps" , "Forts in cities for protection and refuge" , "Fortresses overlooking cities" , "Strongholds for shelter during battles" , "Dials etc up for fortresses" .)