Follow the Isberg Pass trail to the vicinity of Isberg Lakes, and follow a drainage up to the ridge between Isberg Peak and Long Mountain. Make a gradually descending traverse northeast, first past Harriet Lake, then around the west side of Foerster Peak. Cross a low saddle on the north shoulder of Foerster Peak, dropping down over talus to a small tarn/lake west of the peak.
This shoulder can also be reached by easy cross-country hiking from the vicinity of Foerster Creek along the Isberg Pass trail. This option is considerably longer (both mileage and time-wise) than the shortcut via Isberg Lakes.
From the lake, ascend grassy slopes and then loose scree and talus up a chute to an obvious notch just east of the summit. (The notch also appears to be reachable from the north if approaching from the Lyell Fork, but would require axe/crampons year-round).
From the notch, guidebooks and trip reports paint a picture of a confusing, intricate route, but it is much more obvious than these descriptions make it sound. Traverse left into a chute
, and follow this up to where difficulties increase. From here, traverse around to the right and make a gradually ascending counter-clockwise spiral
up to the summit.
The route is easy third class. The moves are simple and most will require no special gear. (That said, they are mildly exposed in places and some trip reports suggest that people occasionally rope up.)