The great American naturalist describes three trips to Alaska -- 1878, 1880, and 1890. It seems his motto was "carpe diem," because he never wasted a moment in which he could possibly hike, observe, measure, or sketch. He also took substantial risks to see as much as he can. He canoed through ice fields; he weathered the Alaskan rain forest without Gore-Tex; he trekked 20+ miles a day over mountains and glaciers. I was kind of gratified when, towards the end of the memoir, he recounts first nearly being crushed between two ice bergs and then falling into a hidden crevasse. I guess this is because I wanted a more explicit acknowledgement that he had been pushing his luck the entire time.
What makes this memoir so great is Muir's prose. He personifies the landscape and gives such a good account of his own elation, it makes you feel as if you are right there with him.