A bit of supplemental info to KenR's post:

Männlichen from Grindelwald. I've ridden this road, and it is fantastic. The views are constantly amazing, and the road is good quality. From what I remember, there's very little riding in the forest: You start off in the holiday chalets near Grindelwald, then go through some farmlands (watch out for the cows on the road), then end up above tree line. Traffic is very light, and what there is drives very slowly. There are a number of unmarked intersections on the way up, but I was able to follow the right road without too much of a problem.

Engstlenalp + Gental. I've read other reports of people who have ridden this road, then from the end of it they have done a couple of kms of pushing/carrying the bike along a hiking trail, then ended up in the village of Tannen. From there, there is a paved road that goes down to Sarnen, between the Bruenig Pass and Luzern. I haven't done this myself, but I plan to do so some day (you can completely avoid the heavy traffic of the Bruenig Pass by doing this).

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Cycling in Switzerland | Photo blog (mostly travel pics from Switzerland)