Travelling overseas? There’s romance about the unknown (6)
I believe the answer is:
flying
'travelling overseas?' is the definition.
(as in flying on an aeroplane)
'romance about the unknown' is the wordplay.
'romance' becomes 'fling'.
'about' is an insertion indicator.
'the unknown' becomes 'y' (algebra).
'fling' placed around 'y' is 'FLYING'.
'there's' acts as a link.
(Other definitions for flying that I've seen before include "Famous train once from King's Cross" , "Getting high" , "In the air; very brief (visit)" , "-- Squad; -- doctor" , "-- Buttress; -- doctor" .)