Goal to travel on inland sea (6)
I believe the answer is:
lagoon
'inland sea' is the definition.
(I've seen this before)
'goal to travel on' is the wordplay.
'to travel' indicates anagramming the letters (I've seen 'travelling' mean this).
'goal' with letters rearranged gives 'lago'.
'lago'+'on'='LAGOON'
(Other definitions for lagoon that I've seen before include "Atoll lake" , "Shallow seaside lake" , "A salt-water lake enclosed by reef" , "Inland sea" , "Shallow salt-water lake" .)