Traveller in a VW (4)
I believe the answer is:
polo
I believe this is a double definition.
'traveller' is the first definition.
(explorer Marco Polo)
'a vw' is the second definition.
(type of Volkswagen)
'in' acts as a link.
(Other definitions for polo that I've seen before include "Equestrian sport" , "Marco" , "car?" , "It's played in water and on horseback" , "Pool (anag.)" .)