Ok, it is not perhaps one of the great railway journeys, but it is one of many I would like to take. The train travels from the main city of Christchurch on New Zealand's south island to the northern town of Picton, where you can then travel by ferry across to Wellington, New Zealand's capital city.
Like most western countries, New Zealand had an extensive network of trains, but many have closed. Sadly you cannot travel by train further south than Christchurch as of 2002 I think. Some might suggest why would you want to travel further south than Christchurch, but Dunedin is a very nice town well south.
The train is called the Tranz Coastal and goes through heaps of tunnels and over bridges, one of which is shared with cars and trucks. I know who would be giving way to whom. But what really appeals to me about the trip is that it travels along the coast with lots of views of the Pacific Ocean.
If you are more an inland person, what about the Tranz Alpine from Christchurch to Greymouth via Arthurs Pass. The train travels through an eight kilometre tunnel up a very steep gradient. Maybe I would like that too, although the Eurostar tunnel under the Channel is pretty boring.
Here are a couple of photos found on NZ tourist promoter sites.