The Grampians National Park is a vast, mountainous and heavily forested area residing a comfortable 3.5 hours drive west from Melbourne. It’s perfect for landscape photography and is extremely popular around Christmas and Easter with up-market accommodation in the very pretty Halls Gap tending to fill up fast. Outside those times you won't have a problem and being a National Park you can always pack a tent and camp in any of the well marked free sites. The park offers some grand views, notably of rocky outcrops and cliff-lines as well as waterfalls and lakes. Native wildlife abounds. So much so, that you'll need slow right down on the roads. Roos and Emus can leap out at any moment. Generally you'll find toilets and picnic tables in most of the marked destinations but often there will not be tap water, so BYO.
In terms of things to go look at, I'd recommend you tick McKenzie Falls, Boroka Lookout and The Balconies first. They are all very accessible, lined up along the same road, basically minutes from the car. Boroka overlooks Halls Gap and its practically a stones throw from the carpark. McKenzie is a steep but short walk, and The Balconies is a couple of kms, but very flat easy walking. If you want a walk taking a couple of hours instead of minutes, head up to the Wonderland area and tick the Pinnacles via Grand Canyon. It's very popular so expect to share the track, but worth the walk and only a short drive from Halls Gap.
After that, if you have time left and still want scenic views, consider the amazing walks around Mt Stapylton in the north of the park. For example, with a couple of hours up your sleeve, start at Flat Rock and head up to to Taipan Wall where the Rock Climbers hang out, then circle around to the summit ridge for amazing views. Alternatively, Mt Rosea in the middle of the park, has some grand views and really isn't that hard a trek, though you'll want to take water and food and have time on your side before dark. Or head south and check out some of the caves and rock art in the Victoria Range. You will need to take on some sandy dirt roads and much longer drives, but there's lots to explore and an endless supply of landscape photography opportunities. Have fun!