Apr 17, 2012 - 11:35 PM
I would opt for Zermatt. It could be a "Brigadoon moment", and I've experienced that...it's worth it. And if you miss seeing the Matterhorn, the town itself is fun. If Jungfrau means the train up to the Jugfrau-joch-I would suggest you take the fennicular at Harder, near the Interlaken Ost train station. There is a great view of the Eiger,Monch and Jungfrau from there-plus some food, frites and beer or wine. You can hike down, if you so desire.
On your way from Lucerne to Interlaken, Brienz is fun to walk around in- the main wood-carving area in Switzerland. Also, the first stop on the boat from Brienz to Interlaken (I recommend the boat rather than the train for that leg of your journey), step off at Geissbach Falls (first stop-just across the lake from Brienz). Classic. You can actually walk behind the waterfall! And if you are really energetic, and have time, hike from Geissbach to Isaltwald and pick up the boat there to Interlaken...so many options, so little time. I envy you your trip-enjoy!