Casks I observed inside port (5)
I believe the answer is:
tunis
'port' is the definition.
(I've seen this before)
'casks i observed' is the wordplay.
I cannot really understand how this works, but
'i' is within the answer.
'casks' could be 'tuns' (tun is a kind of cask) and 'tuns' is found within the remaining letters.
This accounts for all the letters.
This may be the basis of clue (or it may be nonsense).
'inside' acts as a link.
Can you help me to learn more?
(Other definitions for tunis that I've seen before include "Capital of a republic in north Africa" , "North African location" , "N African port" , "Tom, Dick or Harry" , "North African city" .)