If you asked me for only one single place to visit on the South Island, I would recommend Aoraki/Mount Cook without hesitation. It has everything — flat plains/valleys, soaring mountains, impossibly blue lakes, rivers, glaciers, and forests. If you want a luxury hotel stay and do not want to do any hard hikes, there’s something for you. If you want something more middle-of-the-road and want to do some easy/short walks, there’s something for you. If you’re hardcore and want tough multi-day treks, complete with backcountry skiing or kayaking, there’s something for you too.