We will be in Davos, Switzerland for a week the end of August. We do plan on a day trip to Lucerne. (long day, but worth it. We have about 3 days left.
Would you suggest Zermatt, Interlaken, or hop the train to Salzburg???
The Berner Oberland (Interlaken, Lauterbrunnen, Murren, Wengen), is only two hours away from Luzern, via the scenic Golden Pass train. You can easily spend three days there, exploring the Schilton, Jungfrau, and the various trails connecting the villages.