We are hunkered down in a valley in the ice - white and blue are the only colours in this otherworldly scene. The overcast sky blankets the black mountains beyond and blends into the frozen surface, making it difficult to judge where one ends and the other begins. There is a loneliness about this cold, surreal space, something that makes life seem insubstantial.
This is what a polar bear must feel like, I think to myself. Then I remember the only predators in this part of the world are cougars and grey foxes that sometimes stray onto the ice in the hope of finding something lost and weak to prey upon. When one of the trekking guides hands me a cup of hot tea and a sandwich, I feel relieved and thankful for the comforts of the civilised world I have just left behind.
I am somewhere along the 250-square-kilometre course of the Moreno glacier in southern Argentina. The 30km trail of ice is one of almost 50 glaciers fed by the Southern Patagonian Ice Field, the world's third-largest reserve of fresh water. It is also one of the most beautiful sites I have ever seen.
My group of four guides and 15 travellers - mainly Argentines and Chileans but also a couple of young Australians and three Spaniards - have been trekking on the ice for about three hours. The surface is schizophrenic, changing suddenly from jagged peaks to soft, curving valleys, and we have to navigate dangerous crevasses and bright blue streams. We are all on the "Big Ice" trekking tour run by the Hielo & Aventura adventure travel company - an all-day trip that includes five hours of walking on the ice. My travel companion Tom and I had signed up for the trip through our hostel in nearby El Calafate, the charming town of wooden shops and cosy restaurants that serves as a tourist base for trips to the glacier and other parts of Patagonia.
We had arrived in El Calafate, named after the bush with yellow flowers and dark blue berries that is common in Patagonia, the day before in one of Argentina's luxury buses. The vastness of the country means journeys between tourist sites or major towns often stretch for many hours, and the transport system caters to this by making the trip as comfortable as possible. On this journey, as we reclined in our black leather seats, one of the attendants hosted a game of bingo, with a bottle of local shiraz to be won. Our basic Spanish left us a little slow and, by the time I called out "bingo", another passenger had beaten me to the prize.
We reached the town by mid-morning and checked into the America del Sur hostel. Attractive with its wood-panelled and beamed ceiling, and cosy with its warm shared kitchen and rustic dining room, the hostel has pleasant double rooms with en suite for those wanting a little more comfort and privacy, or dorm rooms for those on a budget. We had left booking the room to the last minute and so shared with two young women, including an American travelling the southern continent for two months by herself.
I have always admired people who travel solo, especially women, and asked her about her experience. "Nothing but wonderful," she says. "I've met fantastic, kind people everywhere I've been. South America has a bad rap for safety, but I never felt threatened." She had experienced her share of surprises, however. One involved Tom, who had the bunk above hers for the night. "Do you remember talking to me during the night?" she asks in the morning, a mischievous glint in her eyes. "No," says Tom, concerned. "You reached down and tapped my nose and muttered something about remembering to pack thick socks for the ice trek."
After sharing the laugh, we said our fare-thee-wells and set off for the glacier by bus, driving the 80km to the Parque Nacional Los Glaciares and its crowning glory, the Perito Moreno. The journey included lovely views of a huge, still lake, Lago Argentino, its pink flamingos and the wilds of Patagonia.
On arrival at the park, we visited the balconies - walkways on stilts that offer stunning views of the face of the glacier. This is where the glacier ends and dumps huge sections of ice into the Brazo Sur (South Arm) of Lago Argentino. The 60-metre-tall, five-kilometre-long wall of ice is nothing short of spectacular. The top is whipped up in snowy white peaks, while the ice below is shocking in its blueness.
"When the ice gets pressed ... umm ... how do you say? ... compacted over the years, air bubbles are squeezed out and the ice crystals get bigger. Water takes in light at the red end of the spectrum, so more water, less air makes it look bluer," explains one of our guides, Calvino, in his heavy Latino lilt. "Beautiful, no? I have been here hundreds, maybe more than a thousand, times and it always looks so beautiful."
Just then, a huge section of ice drops from the face, making a thundering sound and huge waves in the otherwise placid lake. "What an incredible sight," says Tom, clicking his camera repeatedly. "Now I can't wait to get out there onto the ice."
We set off on a short hike through alpine, mossy woods to reach the entry point to the surface of the glacier. After the guides fit us with crampons and check we are properly weather-proofed against what looks like a rainy sky, we take our first steps. The heavy crampons strapped to our walking shoes offer us grip on the ice, although any steep slopes still make me feel uneasy as I expect to lose my footing and plunge face-forward. Every step brings an audible crunch. We make our way further onto the ice until there are no signs of human existence. With my ears muffled in a woollen hat, everything is quiet. It's a silence I could grow to love. I ask Calvino if anyone ever comes for longer treks on the ice.
"Si, of course. Some of the other guides and I sometimes spend three, four days on the glacier, camping and ice climbing." I get the feeling he would rather be off there in the emptiness, rather than here with us tourists, who must look so clumsy on the ice. "But I get to come here almost every day with this job, so I am happy," he adds.
We walk on, with each step feeling more at ease. The guides know the route, but the ice can shift so go on ahead to make sure the surface is stable. We stop to look down a room-sized well, the bottom only just visible, and to help each other up steep slopes and to jump across rivers. We could almost be on another planet, the environment is so bizarre. After stopping for our reassuringly ordinary lunch of tea and sandwiches, we continue on the circular route back to the starting point. It's been five hours, but it feels like two.
The trip ends with a boat ride along the face of the glacier, where we get to admire the stunning beauty of the ice formation for one last time. Out on deck, Calvino, his long ponytail trailing out of the back of his beanie, hands Tom and I a whisky, a large chunk of ice rattling against the glass. "It's ice from the glacier, thousands of years old," he says.
We say cheers to Calvino and Perito Moreno and take a sip of the whisky, chilled from the ice but the flavours opening up warm in our mouths. It's been an incredible day and, from the smiles on the faces of the rest of the group, everyone feels the same way. Maybe they also, like me, know that every now and then, when they hear the sound of ice cubes in a whisky glass, they will think of Perito Moreno and its ancient beauty.
WHERE TO STAY
America del Sur Calafate
Has lovely views of the lake and surrounding hills from the cosy shared kitchen. Service is helpful and friendly. There are dorms and private en-suite rooms at this budget-conscious lodging. www.americahostel.com.ar 
Relais & Chateau hotel EOLO
Patagonia's Spirit is situated in the wilderness, 30 minutes outside of El Calafate. The setting is nothing short of breathtaking, and the hotel excels in understated luxury. www.eolo.com.ar 
HOW TO BOOK
To book your ice adventure, e-mail email@example.com , call (02902) 492205 / 094, or visit Minitrekking & Safari Nautico, Av. Libertador 935, El Calafate. For more information on the excursion, visit www.hieloyaventura.com