The Fuhrer Finger is a very enjoyable route with glacier travel, 30-45 degree snow climbing. The route is a good choice for a car-to-car Rainier ascent but it makes for a long day. The Finger is also an excellent ski or board descent route. The routes namesake, the "Finger", is a snow couloir above the Wilson Glacier. The Finger involves about 2,200ft of 40-45 degree climbing before it joins with the upper Kautz Glacier route at approx 13K(a few exposed bivy site here). Once above 13,000ft the slopes ease back considerably and there are a few large crevasses that in late season may require lengthy end-runs to get around. The final slopes lead to the crater rim. I find it best to stay on the flat terrain just outside and below the crater rim and traverse around left and then up onto Columbia Crest. The route is pretty straight forward but there can be a few routefinding challenges crossing through the Wilson Glacier to access the base of the couloir especially around the bergschrund. Upon reaching high camp it may be prudent to gain a vantage point allowing one to scope out a feasible path through the crevasses of the Wilson so as to save time in the early morning darkness when making the way across.
The area of the mountain above this route gets very early sun and there is rockfall hazard in the couloir, a very early start is recommended so as to be in the upper part of the couloir before the suns warming rays loosen frozen rock. As with any snow slope of that angle, there is avalanche hazard.
Park at Paradise 5,400ft and hike the Skyline Trail to Glacier Vista overlook at 6,300ft. This is the rope-up point for teams. Drop down several hundred feet onto the Nisqually Glacier and cross the glacier to the base of a snow gully angling up and right, gaining about 700ft elevation. There is rockfall and avalanche hazard in the chute, move quickly, there is a good safe place to take a break at the top. There are bivy sites here but it is recommended to continue up to the Wapowety Cleaver and follow the crest of the cleaver to a suitable high camp(many rock windbreaks) at the edge of the Wilson Glacier.
Descent- There are really three options, two of these options bring you back to high camp, alleviating the need to carry-over all equipment, the third does not return to camp and requires a carry-over. Option(1) is to descend the climbing route, the drawback to this is the ever increasing rockfall hazard of descending the route after the sun has been up for a significant period of time along with crossing the Wilson Glacier in warm temps/soft snow conditions. Option (2) is to descend the Kautz Glacier route and back to camp. This has become a popular way to return to camp and cover new terrain on both ascent and descent but while there is slightly less rockfall hazard on the Kautz route one must walk underneath the looming Kautz Ice cliff and be exposed to icefall from this feature. Move very quickly here. Note- climbers using the Kautz descent route should be comfortable descending 50 degree alpine ice for a few ropelengths. Option(3) Carry-over to the summit and descend either the ID or DC route back to Camp Muir, down the Muir snowfield, and to your vehicle at Paradise. I prefer option 3 as it also affords one the opportunity to make camp on the summit, an experience that I highly recommend, but is not nessecary as a fit team should have no problem doing the carry-over and descending all in the same day. The optional summit bivy also allows for a very early start to the descent down the DC, getting you well ahead of any guided parties that will be descending en masse later in the day.
A few pickets & runners. Helmets highly recommended as there is rockfall hazard on both the approach and the route.