Came across shelter inside trading area (6)
I believe the answer is:
market
'trading area' is the definition.
(I've seen this before)
'came across shelter' is the wordplay.
'came' becomes 'met' (meeting is a kind of coming).
'across' means one lot of letters goes inside another.
'shelter' becomes 'ark' (I have seen 'Ancient shelter' mean 'ark' so perhaps 'shelter' could also mean 'ark').
'met' going around 'ark' is 'MARKET'.
'inside' is the link.
(Other definitions for market that I've seen before include "Advertise, promote" , "Trading place" , "Outlet for goods" , "World of commercial activity" , "Bazaar" .)