Aoraki Mount Cook
This 50 km drive along Mount Cook Road, State Highway 80, along with Milford Road to Milford Sound, is probably the highlight of driving tours around New Zealand. Driving below the Ben Ohau Range along Lake Pukaki and down the valley towards Aoraki is stunning. Especially in winter (or anytime after snow), so long as you can see the mountains! As you approach the end of the road, Aoraki looms up and provides dream photo ops for Instagrammers.
Once you are there, stay a night or two. There are several options from camping to the Hermitage Hotel, with a nice museum commemorating the life of Sir Edmund Hillary.