Hi dasel, and welcome to MySwissAlps!
Your itinerary generally looks pretty good.
>> Dec 24th: drop by the Lucerne Christmas Market at the Train Station
This one is very small (about 10 stands) and closes at 16:00, so make sure you get there well before that!
>> walk around Lucerne (what sites are worth visiting?
Given the timing, I would suggest a stroll across the Chapel Bridge and other bridges, the old town and lakeside promenade on the opposite side of the river from the railway station.
The "City Guide" PDF on the page below has a map with a self-guided walking tour marked. It's across two pages, so viewing the PDF in "Two Page View" makes it easier to see.
Frommers also has directions for a walking tour:
www.frommers.com/desti nations/lucerne/walkin g-tours
>> Dec 25th: Visit Mt. Pilatus or Mt. Rigi R/T via Vitznau on boat and train?
You wouldn't be disappointed with any of these, and they are all scenic, but at different altitudes, which makes a difference to the terrain on top. The following pages will help you decide what you personally prefer, and how to get there:
The cogwheel train from Alpnachstad to Pilatus won't be operating, but you can go up and back on the cableway from Kriens.
>> Dec 26th: take the train to Grindelwald (what do you recommend doing on this day?
There is information here to assist you:
>> winter hiking
The local tourist office (and probably also your hotel) will be able to give you advice about which trails are groomed for winter hiking.
>> will we be able to do this with the Swiss Travel Pass?
You can download a map from the link below, showing what is covered by the Swiss Travel Pass.
As explained in the legend on the map, red lines are trains, yellow lines are buses, black lines are cable cars, white lines are boats. Solid lines are free, dotted lines are discounted. Discounts are mostly 50%, but only 25% for transport where you see the number "1" inside circle near the dotted line. There are a few grey lines on the map as well, which indicate transport that is not covered by the Swiss Travel Pass. Dashed red lines on the map are railway tunnels, and are on routes that are free with the Swiss Travel Pass.
>> My friend also recommended Mt. First and Schynige Platte, but I'm not sure how to fit this into the itinerary.
The train from Wilderswil to Schynige Platte will not be operating. It closes for the winter and doesn't reopen until 26 May next year.
The gondola from Grindelwald to First is operating (last trip down is at 16:15, but check this yourself on the day to be sure). As it is in Grindelwald where you are staying, you can probably fit it in somewhere.
>> Thank you so much for your help, and Happy Holidays! :)
You're welcome! Happy Holidays to you too, and have a wonderful honeymoon!