Host of castle whose outside is inside (9)
I believe the answer is:
innkeeper
'host' is the definition.
(I know that host can be written as innkeeper)
'castle whose outside is inside' is the wordplay.
I cannot quite understand how this works, but
'castle' could be 'keep' (keep is a type of castle) and 'keep' is present in the answer.
'inside' could be 'inner' (similar in meaning) and 'inner' is present in the remaining letters.
No letters remain.
This explanation may well be incorrect...
'of' acts as a link.
Can you help me to learn more?
(Other definitions for innkeeper that I've seen before include "Manager who made extra provision for visitors" , "For example, Mistress Quickly" , "Accommodating type" , "Pub licensee" , "Job" .)