Wengen to Lake Lucern day trip?

Kim, I did a fairly similar day trip only in reverse...left Lucern early in the morning( first train out ) and headed to Interlaken, then to Grindelwald, up to Kleine Scheidegg and Jungfrau, then back to Lucern that evening. It's a long day but absolutely doable from Wengen to Lucern. The Golden Round Trip to which you refer is certainly a great way to spend a day, as is just strolling around Lucern itself. By the way, you can do the Golden Round Trip ( Pilatus...gondola, cog railway, boat cruise ) in the reverse order as well, and that may work better for you. The route I took when I did the Pilatus trip was start with the ferry ride (the departure point is only a short walk from the train station). Then you get off at Alpnachstad and take the cog railway to the top of Pilatus, and cable car/gondola back down the other side into Lucern. You will have a 10-15 minute walk from the gondola to a local bus stop to get the bus back into Lucern, but the walking route is well marked and you'll have no trouble finding your stop ( the bus ticket I believe is included in the cost of your Golden Round Trip pass but double check to be sure when you first book your tickets at the ferry ).
So if you plan on doing it, I recommend getting the first train leaving Wengen ( around 6:00 or so I would expect, but check the Swissrail site... )

Kim, Glenn has given the advice I would have, just remember it will be a long day. You could shorten the day by returning from Lucerne via Berne that route is a little quicker. Check the train times on the Swiss Rail website www.sbb.ch/en and enter "Bern" in via box. Seeing the time of year you are there I would also check that the train up Pilatus and the cable cars are still running.

Thanks so much for the information. I figured it would be a long day, but from what I've read it seems too beautiful to pass up. My research showed that everything still runs until the end of October and we will be there from September 28-October 5. Appreciate the suggested logistics of taking the boat first!

Lake Luzern is beautiful but so are Lakes Thun and Brienz which are only about 30 minutes from Wengen instead of 2 hours...and you'll pass right by them as you head out of Interlaken to Luzern. Pilatus is nice, but if you're staying in Wengen then you've seen plenty of magnificent alpine scenery. If you insist on taking a long day trip then go somewhere different than where you already are. Try Montreux and the beautiful vineyards along Lake Geneva with the mountains in the background.

Montreax & Lake Geneva...how long would it take to get there by train? I like that idea.

Kim As you are staying in Wengen the trip to Montreux, I would not add another hour each way on a long train journey by adding Geneva to the day out. Montreux is another lovely rail journey if you go to the Swiss Rail website www.sbb.ch/en and in put Wengen and Montreux and vis Zweissemmen, (I think the spelling is correct) it will give you all the information you need including fares, bw warned though the site defaults to the half fare price.