Most travellers en route between Adelaide and Melbourne pass through southeast South Australia as quickly as possible, which is a shame, as the coastal route offers wild, pristine beaches and tranquil fishing villages, while inland there are a couple of brilliant wine regions.  The Princes Highway (Highway 1) is much less direct than the Dukes Highway but far more interesting. It follows the extensive coastal lagoon system of the Coorong to Kingston SE, and then runs a short way inland to the lake craters of Mount Gambier before crossing into Victoria. There’s another possible route on this last stretch, the Southern Ports Highway, which sticks closer to the coast, plus a potential detour along the Riddoch Highway into the scenic Coonawarra wine region directly north of Mount Gambier.