Here is a secret that might surprise you: Milford Sound is actually not a sound at all. Geologically speaking, it is a fjord. A sound is typically a valley that has been flooded by the sea because of a rising river, whereas a fjord is a deep, U-shaped valley carved out by massive, ancient glaciers over millions of years. When the glaciers retreated during the last ice age, the Tasman Sea rushed in to fill the gaps, leaving behind these sheer, vertical cliffs and the fifteen-kilometer-long inlet you see today. Why the wrong name, then? In the year 1823, a Welsh sealer named John Grono arrived here and named it Milford Haven after his home in Wales; later explorers added the word 'sound,' and despite the geological correction, the name stuck for nearly 200 years.