Need quick day trip - tomorrow- from Luzern to xxx?

In one full day, I would head to Rigi: boat to Vitznau, train up to Rigi Kulm, then down to Rigi Kaltbad, cable car down to Weggis and boat back to Luzern.
If you want higher mountains (Rigi is about 1 mile high), take the train to Engelberg and head up Titlis.

In one half day, I would head up Pilatus.

Interlaken is too far for a day trip and not close to the mountain valleys that you really want to see. It's well-known because it's a jumping off point at the foot of the mountains, but not actually in the mountains. You'd eat up a lot of time just getting there and back. Luzern itself is plenty scenic (try a cruise on the lake) or go up Pilatus or Rigi which are pretty much right there.

Thanks - I think we're looking to just train back and forth somewhere with interesting views.

We toured to Mt Pilatus yesterday - and lake tour today.

2 hours on train one way would be ok.

Next day have long trip to Bari, IT.

So, Rigi and Engelberg look close and easy - trainable?

Engelberg is a 43-minute train ride from Luzern, with no transfers.

You can reach Rigi via Weggis by taking a train tomKüssnacht am Rigi and bus to Weggis from there ( 45 minutes total) then walking through town to the cablecar up to Rigi Kaltbad. There is nice hiking up there..

Do you have a Swiss Travel Pass or half- fare card? Rigi is covered with the STP, Pilatus is half price.
Also, a shorter trip is Mt Stanserhorn, the open air Cabrio cable car, (quick train, cogwheel, and cable to the summit )takes 45 minutes each way. It's nice 360 degree view for a sunset, and there's food at the summit. This is also covered by the STP.
Walk along the town wall.
Lunch on the rooftop deck of the Manor Dept store.
Happy hours at the Hotel Gutsch above the city. Looks like a castle at the far end of the city.
Check TI for walking tour.
Check which days are farmers markets.
Enjoy one of my favorite places!

No STP ... we had to extend in Luzern to align with BB in Martina Franca, so hadn't made arrangements ...

you could take the Zentralbahn (narrow gauge, often on the rack - cogwheel) towards Interlaken and get off when the train climbs down the cliff and stops to turn around at Meiringen.

On the way there sit on the right and you will see the beautiful Brünig Pass towns and villages and lakes and mountains, and you can look across shortly after departure at the end of the bit of Lake Lucerne nearby. You climb up from Luzern and down again towards Meiringen. As you start down you get a great view of Lake Brienz - the Brienzersee - and the waterfall of Giessbach from the top all the way down as it falls into the Brienzersee.

Because of time I'm not suggesting to visit Brienz - where the woodcarvers carved the bears and other animals known as Black Forest carvings even though the Black Forest is a couple of hours north in Germany - nor continue along the north shore of Brienzersee with its beautiful views, nor taking a boat on that lake.

In Meiringen (the home of, and the namesake of Swiss Meringue) is a lovely town with a Sherlock Holmes museum because the very close Reichenbach Falls is just on the edge of town, and is the real life cliff where the fictional Holmes and his nemesis Moriarty fought to the end. You take a funicular up there, or reach the waterfall by Postbus, or you can - if very fit - hike.

Then back on the train and back to Luzern - sit now on the left for the same great views from the opposite direction, the views are somewhat better than from the other side IMHO.

Another maybe less obvious idea: Go to Ballenberg. Is near Brienz, use www.sbb.ch or the app to figure out how to get there.

Ballenberg is an open air museum with lots of lovely old Swiss buildings, and demos of what country life in Switzerland use to be like.

good idea WengenK just one stop beyond Meiringen on the same train from Luzern ....

BUT

both my and your suggestion, WengenK would blow a fuse because of the EV (replacement bus) due to the track work around Giswil.

Both of these suggestions won't easily work this week.

The works around Giswil won't make this impossible. Looking at www.sbb.ch I see a trip duration of 1h16 min for Luzern - Ballenberg West, and that is about the same as it would be had the train be operating as normal. Just that a part is by bus...

that's good to know ... that does bypass Meiringen though I guess. I wonder if it comes down the switchbacks above Brienz or if it has a back route that I don't know....

Well, shoot ... wife didn't feel like a day long excursion so we enjoyed the glacier museum, some walkabout, and snacks and beer at a lakeside cafe. A great "down day" prior to train at 0618 tomorrow - Lugano, Milano Centrale and Bari.

Thank you all for you help - will hit another mountain or two next trip!