Quickly look around tower in a castle (4)
I believe the answer is:
keep
'tower in a castle' is the definition.
'keep' can be an answer for 'castle' (keep is a type of castle). I am not certain of the 'tower in a' bit.
'quickly look around' is the wordplay.
'quickly' becomes 'kee' (I can't explain this - if you can you should believe this answer much more).
'look' becomes 'spy' (spy can mean to look or see).
'around' means to look at the middle letters.
The centre of 'spy' is 'p'.
'kee'+'p'='KEEP'
Can you help me to learn more?
(Other definitions for keep that I've seen before include "strong position" , "Retain; stronghold" , "Retain; strong tower" , "Board and lodgings, perhaps" , "Castle tower; cost of maintenance" .)