Giant Gate Falls is a stunning waterfall located near the end of the famous Milford Track. (A 4 day, 53km hiking experience!) Taking a water taxi to and from the end of the Milford Track and walking to Giant Gate falls is a fantastic way to spend a few hours (3hours return) before or after your cruise.

Make sure you turn around and return the way you came once you reach Giant Gate Falls! You don't want to accidentally continue along the Milford Track.
You must book a water taxi (approx $50 return PP) to reach these falls and it is very wise to let your taxi operator know you are just visiting the waterfall for a day hike, that way they will know to look out for your return the same day at your pre booked time.
- https://www.fiordlandoutdoors.co.nz/transport-and-experiences/milford-track-day-walk/milford-track-day-walk-milford-sound/

New Zealand Wanderer has a very detailed blog about visiting this waterfall on a day hike that I would recommend reading before you visit.
https://newzealandwanderer.com/giant-gate-falls/#How_to_Get_There