Shuffling along inside a deep crevasse on a glacier moving at the rate of one to two metres a day is not for the faint-hearted ... so I wondered what the heck I was doing there.
The crevasse was so narrow our booted, cramponed feet had to master the pinstep - taking tiny steps, moving one foot forward and then bringing the other one up behind it, not ahead of it - while rotating the upper body 180 degrees to be slim enough to squeeze along the gash in the glacier.
It was a surreal and slightly unnerving experience, exploring Franz Josef's chilly blue-white marble intestines.
The occasional distant cracking sound did nothing to allay my fears of becoming a human sandwich inside two enormous slices of ice.
But Tim Bluett, our guide on the Glacier Explorer heli-hike expedition, was a safety fanatic who constantly checked our crampons, redrilled ice screws, tested fixed lines and kept us strictly to the track, so he inspired my confidence.
And as we climbed higher, I was so mesmerised by the maze of crevasses, caves, bizarre ice sculptures and sharp peaks like stiffly-beaten egg whites, I completely forgot to be nervous.
At the highest point of our climb, 700m, we reached "the Pinnacles" and could see into the most dramatic, active part of the millions-of-years-old mighty river of ice as it strained and fractured, grinding its way down the valley.
Apart from his impressive prowess at wielding a hefty ice axe and shovel, Tim was also a veritable font of knowledge.
As we gazed at the dazzling landscape bathed in winter sunshine, he told us all about the Franz Josef, the world's steepest and fastest-flowing commercially-guided glacier.
It descends from a height of 3000m above sea level to 350m in as little as 11km, moving at a rate of one to two metres a day in the winter and three to four metres a day in the summer.
The Franz is New Zealand's fourth largest glacier. It's also one of the most accessible glaciers on the planet, terminating in lush rainforest at 350m above sea level just 18km from the sea.
Despite advances in 1983 and 1999, overall, the Franz Josef has retreated about three kilometres since the late 1880s.
Since 2008, the glacier has been in major retreat mode, losing 800 metres in length. In 2012, a dramatic change occurred.
A hole in the ice resulted in the loss of over 250m from the terminal face in just over 12 months, leaving it unstable and unsafe for hiking.
Helicopters are now the safest way to explore this awe-inspiring natural phenomenon.
High on the glacier, Tim also told us the legend behind the Maori name for the glacier - Ka Roimata o Hine Hukatere; The Tears of the Ice Maiden - handed down to him by Ngai Tahu, the kaitiaki or guardians of the land.
It's a love story about a beautiful Maori maiden whose lover Wawe fell to his death while climbing with her.
The gods turned Hine Hukatere's tears into a river of ice to preserve Wawe for eternity.
We also learned that glacier guiding is New Zealand's oldest adventure tourism industry, pioneered in the early 20th century by brothers Peter and Alec Graham of Franz Josef.
After a spectacular afternoon on the ice, the throbbing sound of chopper blades filled the valley.
We lifted off as the sun began to fall from the sky and the snowy peaks turned pink and gold in the sunset.
Within five minutes we were back at Glacier Base where we soaked in hot pools surrounded by rainforest, the perfect finale to an unforgettable day.
- Justine Tyerman did the four-hour Franz Josef Glacier Explorer heli-hike expedition and visited Glacier Hot Pools and Spa courtesy of Ngai Tahu Tourism - website: ngaitahutourism.co.nz - which owns Franz Josef Glacier Guides NZ - franzjosefglacier.com. JUCY Rentals provided land transport - jucy.co.nz. Air New Zealand flies direct from Auckland to Queenstown - airnewzealand.co.nz.