After getting a monthly doze of adrenaline on Mt. Robertson, next day I was looking for an easy peak with little exposure and difficulty. For some reason, I thought Big Sister fits this description. I didn't do any research and just followed a distinct trail (there are 2 trails as I later learned). Big Sister turned out much harder than expected. There were two brief Class 4 sections on good slabs and the well-know Class 3 downclimb before the summit block. The rest of the terrain above the treeline (steep scree and slabs or usually the both) required some caution. It looked like a solid "difficult" scramble. I was probably off-route but, curiously enough, I followed a path with cairns and flaggings and other people followed the same route.