Detailed exhibit about old place in London (4)
I believe the answer is:
soho
'in london' is the definition.
'detailed exhibit about old' is the wordplay.
'detailed exhibit about' becomes 'soh' (I can't explain this - if you can you should give a lot more credence to this answer).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'soh'+'o'='SOHO'
'place' is the link.
This may not be correct. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for soho that I've seen before include "Nightclub area in London" , "District of London, noted for restaurants and nightclubs" , "capital district" , "Colourful neighbourhood in London's West End" , "Exotic London district popular with tourists" .)