Australis is a big, rough country. The biggest island in the world with a hot climate. Before you visit, you should have some idea as to what attracts you. Make sure you wear plenty of sunscreen & a hat. And, sure, carry water.
If you would consider city scapes to be landscapes, but there are plenty of landscape type opportunities in and around the Sydney CBD. A walk through the Darling Harbour district, around beneath the Sydney Harbour Bridge, across the front of Circular Quay, around the Opera House promenade, through the botanical gardens, and around to MacQuarie’s Chair will yield plenty of scenes. The National Parks and beaches near there will provide some great images.
Around Sydney try the Harbour Walk all along the northern shore, or as already mentioned there are hundreds of trails in the Blue Mountains (but it is very easy to get lost, or worse).
Then you’ve got Bondi, and/or Manley beaches and their surrounds (both only a jetcat away).
If you want to get right out of Sydney then consider the “Blue Mountains”. A couple of hours by car, but totally different scenery. Probably best done as an overnight stay.
The Great Ocean Road (which is west of Melbourne) is excellent. Do it as a several day trip from Melbourne. You go right through the Otway Ranges rainforest along the way. At the Apostles there are great views from sea level via the Gibson Steps. The 12 Apostles is the main attraction, but that entire coastline can provide countless landscape / seascape views. Also around Melbourne the forests around the Black Spur are very nice. Probably best enjoyed as an overnight trip from Melbourne, i.e. drive west for a day, stay over in one of the many B&Bs, and drive back the next day.
In the far north, which is rough country, with gorges, lots of wildlife, the Kimberley and the also the Bungle Bungle is an interesting area to see.