Here is the Routeburn track! Its one of New Zealands Great Walks and features alpine scenery and a lot of lakes! Also check out the Kepler Track:
The Routebourne Track has wonderful landscape and offers incredible views into the heart of the New Zealand Alps. On the other hand it is a one way trip and you have the problem of getting back to your car from the end of the Trail. That's why we did it on two day trips and just walked in from one both sindes and returned. Unfortunately you miss out a part of the trail in the middle as it would be too far to walk in and out in one day.
Part 1 - Lake Harris
The first time we walked the trail from the Mount Aspiring NP/Queenstown side. We made it a day trip up to Lake Harris and back. We wanted to walk up to Harris Saddle but didn't have enough time as we had a late start. We had a wonderful picnic by the lake and got some pretty nice shots of the mountains mirroring in the lake and the view down the valley. It was a nice hike although we were happy as we arrived back at the car after the long walk through the forest at the end.
Part 2 - Key SUMMIT
The next time we walked the trail from Fiordland NP part. We walked up Key Summit and made a second stop over at Lake Howden. We had lunch there but didn't walk further in as we wanted to see the sunset at Milford Sound later. Lake Howden is nice but as everywhere on the West Coast Sandfly alarm. Key Summit is a must visit when driving down to Milford Sound. You have a 360 degree panorama view of Fiordland Mountain scenery and from morning to noon the reflecting mointains in the little tarn up there make a beautiful picture. On the trip you get views into Hollyford Valley and can get a glimpse of Lake Marianne (We highly recommend to do this track as well - its quite beautiful).