Shilthorn to Lauterbrunnen

You would take a gondola up to Muerren from Laut.., yes walk down the trail to Gimmelwald then board the gondola/cable back down to Lauterbrunnen. all easily done.

The Schilthorn cable car does not go to Lauterbrunnen. It takes you to Stechelberg which is up the valley from Lauterbrunnen. You will either have to walk or take the bus back to Lauterbrunnen. You could, however, get off the cable car in Murren and take the train/gondola combo back to Lauterbrunnen. (which is the way you are coming up if I understood you correctly. You catch a gondola in Lauterbrunnen and then take the Panorama train to Murren.)

These responses are a little bit confusing. The Schilthornbahn (cable car) starts in Stechelberg, and goes to Gimmelalld (where you change cars) then Muerren, then Birg then up to the top. Coming down is the same.

If you are going to Lauterbrunnen from the top, you can either (1) get off in Muerren, and take the train/calbecar combination via Grutschalp down to Lauterbrunnen, or (2) stay on the cable car to Gimmelwald, do the short switch there, and ride down to Stechelberg (this section is one of the most exciting cablecar rides anywhere). There, at Stechelberg, you take a short Postbus ride back to Lauterbrunnen. Or you can walk. It's a nice walk.

From Muerren on down, it's a diamond-shaped route. Either way, you do 2 sides of the diamond to get to Lauterbrunen on the diagonal opposite corner. It's nice to do it both ways at some point on your journey.

Just as a coda to Lola's post: the walk from Stechelberg, down in the valley, is flat.

You can also walk down from Brig (steep but not scary steep for most people) or even the top (scary steep) to Murren and Gimelwald.