1. West ridge Class 4. From the vicinity of Gentian Pass, wander up the easy west slopes of Polemonium Ridge to the summit of Polemonium, then descend a loose 3rd class gully to the scree below Polemonium's S face cliffs. Alternatively, traverse snow on the north side of Polemonium and deke through the Polemonium-CT notch to gain the same location. Hike and scramble up scree and short rock bands on thewest ridge of Castle Towers to the west summit. Descend 4th class ramp on the NE side of west summit to gain the west-central summit notch; traverse loose blocks and large holds around the N face of the summit tower to finish up to the summit via the east side.
Equipment: Rope and a few slings
2. South Couloir 4th class . Easiest route under spring conditions when approaching from Sphinx Hut. From Sphinx Glacier ascend snow (45-degree) at the base of the couloir at GR041316 on 92 G/15. Scramble very easy but very loose rock to the gap between the West and the Main Peaks.
Scramble up the west-facing (easy) side of the gap to just below the summit tower. Traverse the top of the Northwest Face along the base of the tower. Scramble up the tower by its eastern aspect.
3. NW Face Glacial ice and loose 4th class mixed climbing. Climb the glacier on the NW face of Castle Towers, avoiding crevasses and bergschrunds, and finish with steepish snow and ice that peters out into easy mixed climbing on large, sometimes loose blocks just below the summit ridge. Numerous finishes are possible so choose whatever line seems feasible and enjoyable.
Equipment: Ice axe, crampons, rope, a few slings, possibly a little bit of rock pro