I am imprisoned in a fortress in Spain (7)

I believe the answer is:

castile

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'in spain' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for castile that I've seen before include "former Spanish kingdom" , "Old Spanish kingdom" , "Elastic region in central Spain" , "Elastic (anag) -- region of Spain" .)

I've seen this clue in The Globe and Mail.

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