I’m also new to this forum, but as experienced traveler can tell, that myswissalps.com is the most helpful source I ever see , where you can get an answer from the real EXPERTS of Switzerland! I think that better wait for their response because it’s always detailed with many useful links provided. Also you can find the information , if you type your question in the search engine at their website. Many travelers shared their experience as well ( of course without advertising of their websites, as I strongly believe is inappropriate).
I also have an upcoming trip to Switzerland (3 nights based in Zurich ) at the end of July /beginning of August & planned my itinerary very careful in order to show to my daughter the most of this beautiful country in such short period of time.We’re planning to spend one day in Luzern as follow:
Early morning train from Zurich to Arth-Goldau, cogwheel ( blue)train to Mt. Rigi, explore there, cogwheel (red) train to Vitznau , boat to Luzern.( of course weather permitting ). This itinerary ( or vice versa ) give you the opportunity to see the mountain & beautiful Lake Luzern from different point of view.
Change boat to Verkehrshaus -Lido ( Swiss Transport Museum) to experienced Chocolate Ride Adventure.( 20 min show to see how chocolate is made).
Take City Train tour (40 min ride on small electrical train starting from Hotel Schweizerhof).
Take 14:02 train to Engelberg to visit benediction monastery (Dated 1120). Monastery has one of the largest organ in Switzerland & the only monastery that has small cheese making factory. There is a dairy show ( approximately every 40 min up to 15:30 pm) inside the cafe with glass wall from where you can see the process of cheese making. After that short tour of the monastery providing by monk at 4 pm ( tour on German language only, but they’re providing booklet on English ).
Back to Luzern by taking 17:02 train.Explore city by walk.
All the above travel covered by Swiss Travel Pass or ( in my case) by Saver Day Pass ( cost 52 CHF per person per day if you buy it up to 60 days in advance , but they’re can be sold out).
This is our ambitious itinerary , but always a good idea to have a back up plan in case of a bad weather.
You can take one of scenic train ride for that day, but better wait for Top Member’s advice (since I’m not an expert). Luzern is one of the most beautiful cities ( in my opinion) and very safe ( as all Switzerland ), and opportunities to spend one day there are endless. Everything up to your interests and willing.
Enjoy your trip!
PS By the time I finished my post, Steph already replied to you. Such an amazing idea to spend a night on mountain ! I wish that I can do it, too. it’s exactly what I mean saying that better to get an advice from real experts