Northwestern New South Wales: See
Lightning Ridge is basically the opal capital of New South Wales (and the East Coast, for that matter) and if you're into mining, then it's a great destination to check out. Cobar is also known for its rich mining history, but is much larger than Lightning Ridge.
For those interested in Indigenous history, Gundabooka National Park has some of the state's most well-preserved petroglyphs. Although the petroglyphs are fairly simple compared to others, it's still an impressive site that's well worth a visit.
Like other places in Outback NSW, there are many homesteads dating from the era of agriculture. The Toorale Homestead is one of the state's largest, and once a part of the world's largest sheep station.