Underneath our feet the ice shifts and sighs. We hear the crack and crash of an iceberg calving in the distance. That's when it hits me - this ice is alive.
Even from afar, the Perito Moreno Glacier is an awesome sight. It stretches 5km across Lago Argentino and 30km back into the mountains. Its sheer front looms 60m above the milky green water. From the viewing platform you can see the intense blue that radiates from within, the spiky white peaks, the brown streaks of sediment that snake through the ice like marble.
This is an active glacier - it moves up to 2m a day - so you're sure to witness it calve if you wait long enough. You'll hear a thundering rumble just before a huge chunk of ice breaks away and hurtles into the lake.
It's an unforgettable experience. But to truly appreciate Perito Moreno, you need to get on top of it.
We took an ice-hiking tour with Hielo y Aventura. After checking out the glacier from the viewing area, we rode a boat across the lake. On the rocky beach, the guides fitted us with crampons and we went out onto the glacier.
From afar the peaks look jagged as shark teeth but in the hike area the ice slopes gently. The multi-lingual guides make sure no one gets lost or hurt. They also point out features like ice caves. After two hours they led us round a corner to...but I won't spoil the surprise.