Running amok, Rambo captures a large, large castle (8)
I believe the answer is:
balmoral
'castle' is the definition.
(Balmoral Castle, royal residence)
'running amok rambo captures a large large' is the wordplay.
'running amok' is an anagram indicator.
'captures' means one lot of letters goes inside another.
'large' becomes 'L' (eg in clothes sizes).
'large' becomes 'l' (eg in clothes sizes).
'rambo' anagrammed gives 'bmora'.
'a'+'l'='al'
'bmora' placed around 'al' is 'balmora'.
'balmora'+'l'='BALMORAL'
(Other definitions for balmoral that I've seen before include "Scottish residence of the British royal family" , "Royal castle in Scotland" , "Royal holiday residence on the River Dee" , "British royal summer residence" , "Royal retreat in Scotland" .)