The Penknife is the long-forgotten and overlooked spire directly north of the Petit Grepon summit. Its summit is just as high (if not higher) and much less crowded than the Grepon. Although short (2 or 3 pitches), the actual climb is really the final phase of a very long and exciting expedition through Loch Vale (read "getting there").
CAUTION: There is a lot of very loose rock on the Penknife! Check every handhold and especially anchors!
There is the "boring way", which consists of climbing the 8 pitches of the Petit Grepon south face, rappelling into the saddle of the two spires, and climbing the Penknife.
Then, there is the "epic route", which consists of hiking, glacier travel, class 4 scrambling, rappelling, and climbing. I strongly suggest staying overnight at the Andrew's Creek campsite (BC permit required and don't forget bug spray!!). Hike up the Andrew's Creek trail to Andrews Glacier. The Glacier is very steep in parts, crampons are recommended but not necessary. After the glacier ends, you must scramble up a HUGE talus field at the base of the Sharkstooth. Your objective is to reach the saddle between the Sharkstooth and the Saber, aka "The Gash". The talus field gets cliffed out in spots so be careful. At the top of the Gash you can see over the horizon into the "Sky Pond cirque". The Penknife is directly in front of you. Scramble down southeast to a ridge between the Penknife and the Saber. From here you will need to set a rappel down onto the grassy plateu on the east side of the Petit Grepon. Once on the grassy area, begin technical climbing.