The majority of the South Island, approximately two-thirds, is dominated by the Southern Alps. This long mountain range starts in Fiordland in the south, reaches a high point at Aoraki/Mt. Cook (3,754m), and descends toward the temperate coastline in the north. The Southern Alps bisect the island and seperate the West Coast from the eastern regions such as Canterbury.
The bottom corner of the South Island is home to the powerhouse Te Wāhipounamu - South West New Zealand UNESCO World Heritage Area. This includes Fiordland National Park, Milford Sound, Doubtful Sound, Fox Glacier, Franz Josef Glacier, Mt. Aspiring National Park, and Mt. Cook National Park. The diversity of landscapes in this relatively small area is astounding.
East of Fiordland is the Otago region and Queenstown, New Zealand's adventure capitol. Central Otago was once the gold mining center of the country. In recent years it has transformed into a hotspot for wineries and biking on the revamped Otago Rail Trail.
North of Otago are the West Coast and Canterbury Regions. The West Coast is known for mammoth glaciers, tall mountains, and wild coastline. Canterbury is home to alpine Arthur's Pass and the recovering city of Christchurch.
The Southern Alps make one last push in Nelson Lakes National Park before dropping down to the clear waters of the South Island's northern coast. The north offers the full range of ocean activities, great seafood, and Marlborough has earned its reputation as one of the world’s premier wine regions, in particular for Sauvignon Blanc. Abel Tasman National Park has white sand beaches and world-class kayaking; the Marlborough Sounds are considerably bigger with more room to explore.
There are many other great places to visit on New Zealand's South Island. On the whole, the towns are small and unobtrusive and the island functions essentially like one big national park. Enjoy the journey.