Adelaide to Melbourne
I had no idea that this was suggested back in 2018. What a shame that it didn't go ahead!
The Marshall government toyed with the idea of building a 1,000km bike path from Adelaide to Melbourne, basically hugging the coast the whole way. It'd be a magic way to spend a couple of weeks, meandering the coast line, eating and drinking the local deliciousnesses. Looking out over the ocean and inland to the massive and diverse countryside that would pass you by.
Ride over. Train back.
Here's an article about the idea's demise.
I don't see the current governments going for it, but I reckon it's worth pushing about.