I am going with Real Journeys to the Glowworm caves of Te Anau.

As Glowworm caves are located on the western side of Lake Te Anau, our visit starts with a scenic cruise across the lake. 

I enter a large hut where we are offered tea and coffee and we can then watch an informative slide show explaining the formation and the glowing process of the glow worms. In fact, the glow worms glow to attract flying insects to eat them.

Then, our guide takes us to the caves and we start to explore it by foot and by boat until the silent darkness of the glowworm grotto. What I see is amazing: it looks like thoudans of stars shining in a black sky. It's so beautiful that I could stay there for hours. For those interested in astronomy, this is a very special moment.