“Follow me,” Kirk Martinez says as he leaps from boulder to boulder, his shoulder-length brown hair trailing behind him. I try to keep pace, striding along the trail, a bitter wind against my face. We stop at the base of a wall of rock that rises more than a thousand meters. From behind that mountain, what looks like a huge river of snow snakes its way to where we stand. But as we move closer, one thing becomes clear: this enormous swath of bluish white is not snow–it’s ice. It’s a bright August morning in the tiny bucolic town of Olden, in southwestern Norway, and I find myself about to clamber up the largest mass of frozen water I’ve ever seen. It’s called the Briksdalsbreen. Breen, I am told, is Norwegian for glacier, and Briksdalen is the picturesque valley where it resides. Although it holds more than a billion tons of rock-hard ice–enough to fill up a thousand Empire State buildings–Briksdalsbreen is just a small arm of a much vaster glacier named the Jostedalsbreen, which, boasting an area of almost 500 square kilometers, is the largest ice field in continental Europe. “Time to put on the gear,” Martinez says, grabbing…