Port Augusta sits at the head of Spencer Gulf, where the desert roads from the north meet the coast and the Flinders Ranges rise to the east. Many travellers treat it as a fuel stop between Adelaide, Coober Pedy, and the Flinders, but it has enough of its own to justify a spare day.
The city's appeal is plain and outback-facing. Wadlata Outback Centre gives a good introduction to the inland routes, Aboriginal stories, railway history, and European settlement. The Australian Arid Lands Botanic Garden is the better surprise: red soil, saltbush, desert flowers, birdlife, and long views toward the ranges.
Port Augusta is not a polished resort town, and that is part of the point. Use it to understand the threshold between settled South Australia and the dry interior, then climb the Water Tower Lookout to see the gulf, railway lines, highways, and low ranges all pulling away from town.