Routeburn Track both ways. 2 days 64 kilometers
Most people complete the Routeburn track one way or connect it to greenstone gables to get back to Queenstown without the mess of hiring expensive transportation at one end of the track.
My hiking partner and I also wanted to avoid the ordeal of organizing transportation at one end of the track so we just decided to walk it both ways. It was worth it. The great walks feel like a luxury after walking some of New Zealand's tougher terrain. The trails are perfectly maintained, there are signs all over the place indicating how far you have gone or how long to the next hut. There is absolutely no way to get lost on a Great Walk trail.
The Routeburn was gorgeous. We lucked out with a blue bird day on the first day then on the way back we had some clouds that covered up a lot of the views. It is a lot of kilometers but with the ease of the trail it is perfectly doable to walk one way in a day. There were quite a few fit trail runners we saw along the way too!