The townships of Te Anau & Manapouri are the gateways to the Fiordland National Park. This park is about 1.2M hectares of area and is the largest out of the 14 National Parks in New Zealand. All these parks are protected by Ministry of Conservation.
Between Te Anau & Manapouri, our choice was to stay in Te Anau as all the tour-operator pick points were in Te Anau and about 5 mins drive from our Airbnb accommodation. Spending 2 nights in the mouth of this National Park can introduce you to the grandeur of Milford Sound, unique nature’s creation of glowworms, over 600 of formed tracks for hiking and many other key attractions! 
How to Get to Te Anau
We landed in Queenstown. We had pre-booked our car with Hertz. There are many rental car agencies at the airport itself so it is very convenient. Since we went in winters we also took snow chains and learnt how to put them on. There are notices all along the road to indicate if the snow chains need to be put on. Snow chains are typically not required for driving to Te Anau but may be required if you are going to Remarables Ski area or Coronet Peak.
It’s a very small airport but Queenstown offers one of the most breath-taking landings with a view of The Remarkables and Southern Alps. I was completely blown away!
Day 1: Gloworms Cave tour
The drive to Te Anau offers splendid panoramic views with raw mountains, fresh water lakes and rivers hustling in the background. Driving along lake Wakatipu and ice capped southern alps for the first 40 Kms was an exhilarating experience. It is a single lane highway with minimal traffic. So you can relax and enjoy the drive. Along the route, there are quite a few lookout locations, shoulders and nicely done resting areas. Stop at some of these to consume the dramatic landscapes. 
While it was intended to be a two hours journey, we took our own sweet time and reached in about 4 hours.
We reached Te Anau by 4 PM in the evening. A small quiet town developed on the shores of this second largest lake in NZ, lake Te Anau, would be a dream-stay for those looking for untouched nature.
It was time to go for the Gloworms Cave tour. It starts from the Te Anau Town Centre and is operated by Real Journeys, a family owned business. The tour includes two 30 minute cruise ride and a 1 hour tour of the caves with the glow worms. It was a very unique experience. The caves form just a small part of the larger Aurora Cave system sprawling 6.7 Kms into the surrounding Murchison mountains. The glowworms in the dark caves looked like stars in a galaxy. They glow to attract the moths and catch them to eat. The tour operators take you through the guided tour inside the cave and share narratives about the formation of caves and the lifecycle of these worms. Inside the cave, there is a 20 minute boat ride to see the glow worms. Photography and videography is prohibited inside the cave. Another interesting fact is that based on the sensitivity of light, each person sees a different color for the worms. Akshat, my husband saw the glow worms as white sparkling objects whereas I saw all of them as emeralds. I will recommend the 4:30 PM option instead of 7:00 PM especially in winters as it might get quite cold inside the cave for the 7:00 PM tour. Do carry insect repellents.
Overall a unique experience but fairly expensive at 80 NZD per person. If you are keen, then highly recommend to pre book online as they get booked pretty fast during peak seasons.
Day 2: Milford Sound
I would highly recommend this to be a self-drive trip in summers! However in winters, check the weather forecast and take a call whether you want to drive to Milford Sound or take a coach. The coaches have glass top so you don’t really miss the mountains, glaciers and lakes. The drive to Milford sound is absolutely gorgeous. We booked seats in a coach as it was recommended by locals and we did not want to take any chance. The coach starts from Queenstown and can be boarded at Queenstown or Te Anau. We boarded it from Te Anau at 10 AM and reached Milford sound at 1 PM with 3-4 stops on the way. The coach was nice and comfortable. The driver guides you through the tour and stops at scenic spots on the way. Enjoy the views at Eglington River, Mirror Lakes, Knobs Flat, lake Gunn en Route to Milford Sound. It will surprise you!
The road leading to Milford Sound was built during Great Depression time and even today roads to Milford Sound have 65% higher chance of accident than anywhere else in New Zealand. It is a world Heritage Site and only in 1954, this 1.2 Km second longest tunnel in NZ was built to access the Fiord. This single lane tunnel is a highlight of the trip as the sealing of the tunnel is very low and just enough for the coach to pass. Once you are through, the jaw dropping vista of the Fiords open up in front of you. My pupils elated with excitement and I was jumping off my seat. It was unbelievable. 75% of this park is not walked by humans due to the sheer size and remoteness.
Many famous movies are shot in Fiordland National Park to capture the intensity of these ranges. When we reached, we were told that Tom Cruise was shooting here for the next Mission Impossible movie!
Once we reached Milford Sound, we took the cruise at 1:10 PM. With numerous voluminous waterfalls, rip-roaring mountains, spectacular cliffs and unique marine life, it is no surprise that Milford Sound is one the New Zealand‘s most visited site. 
We started our return journey at about 3 PM and reached Te Anau at 5: 15 PM. In hindsight, I would have really preferred to self-drive but even driven in a coach was a memorable experience.