Overview & ApproachThis route is quite an enjoyable climb and well worth doing; great views of Mt Baker to the NE, the wonderful rough texture of the rock (olivine - dunite) and the opportunity to climb two interesting peaks in one trip. schitthaedt has provided excellent directions for the approach to the North Twin Sister here (these directions work equally well for the South Twin Sister too).
To reach Sisters Cirque follow the logging road to it's end at a logging landing. At the far end (S end) of the landing there is a trail (on the uphill side) that traverses across the clearcut bearing SE. The path stays nearly level, but at spots enters the timber above it, crossing the 1/2 to 3/4 mile distance to the entrance of Sisters Cirque. When making the traverse (in either direction) DO NOT descend below the level of the logging landing but maintain your elevation slightly above (the landing).
Route DescriptionFrom the entrance to Sisters Cirque climb E up into the beautiful basin (see photo above) below the peaks and continue (E) to the headwall between the North and South Twin. Fred Beckey (in his CAG - Rainy Pass) suggests climbing the headwall at the lowest point; we found the rock rotten at that point and opted to cross at a point farther N on more solid rock. Nice camping spots can be found in the cirque but for more expansive views continue over the headwall to Sisters Glacier.
From Camp (on Sisters Glacier) cross (the Glacier) SSE to the E side of the Toe on the NE Ridge (moat crossing later in the year). Once upon the NE Ridge the scrambling / climbing is directly up (on or near to the crest of) the ridge to the summit. The nature of the route and rock provides ample lattitude for climbing. There are some loose rocks along the way; keep the party close together.
Descend the route.
Essential GearThe route is 3rd class. Rope, ice axes, helmets, slings; the route does traverse the Sisters Glacier for a 1/4 mile, though we didn't encounter crevasses earlier in the year. Mountain bikes for the approach and the descent, leave your bike as high up as you can on the logging road (30 min or so bike descent!).
This route is an excellent one to do in combination with the South Face route (one class 4 section in late season) on the North Twin.