Old marketplaces in lagoon's prime locations are chaotic (6)
I believe the answer is:
agorae
'old marketplaces' is the definition.
(I've seen this in another clue)
'lagoon's prime locations are chaotic' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'are' is 'rae' which is within the answer.
The remaining letters 'ago' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'in' acts as a link.
Can you help me to learn more?
(Another definition for agorae that I've seen is " markets".)