In the Jungfrau region:
From Grindelwald up to the First by gondola, then hike over to Grosse Scheidegg, down into Rosenlaui (stay there) then to Meiringen and the train.
From near Lauterbrunnen to the Lobhornhut - really nice day hike with spectacular views and a great farm with fresh cheese to buy along the way. Or stay there and continue on to Saxeten.
From Mürren (can take the tram from Lauterbrunnen, one valley over from Grindelwald) to over Sefinenfurge to Bundalp (place to stay), from there to the Blumlishorn hut (another night), then down to Kandersteg to the train. Quite a bit more ambitious but very nice.