Hello AusieSue
With a Saver Day Pass, you could continue from Lauterbrunnen with the postbus to Stechelberg, take the world’s steepest cableway to Mürren, the train to Grütschalp and another cable car back to Lauterbrunnen.
You could also take the boat from Interlaken to Brienz in the afternoon (last departure 4 pm but verify the timetable) and the train from Brienz to Lucerne.
Kind regards
Danhiel