Where travellers accumulate strain that can't be recovered from? (3,8)
I believe the answer is:
air terminal
'where travellers accumulate' is the definition.
'strain that can't be recovered from?' is the wordplay.
'strain' becomes 'air' ('air' can be a synonym of 'strain').
'that can't be recovered from?' becomes 'terminal' (as in a terminal illness).
'air'+'terminal'='AIR TERMINAL'
(Other definitions for air terminal that I've seen before include "part of Heathrow" , "place to start journey" .)