Christmas Day in Switzerland

Our experience with Christmas Day in Germany was that everything except for the beer halls were closed. I would plan on a picnic in your room for Christmas day plus an afternoon visit to the a close beer hall. It will be packed but find a table and crowd in. Another time in Spain (Seville) everything was shut down by 6 pm on Christmas eve and stayed closed through Christmas day. The exception were the restaurants associated with hotels. The lines were very long for these restaurants.

I would expect many restaurants to close early or be closed entirely on Christmas Eve as well as Christmas. Dec. 26 is also a holiday in the Alsace area (not sure about Switzerland) so expect closures that day as well.

Christmas Day is a Sunday this year, so many businesses and restaurants will be closing early on Dec 24 and remaining closed until Dec 27. Perhaps hotels with in-house restaurants might have a Dec 25 dinner. What type of lodging will you have?
Whether you are religious or not, attending a service in a historical church could be quite festive with the beautiful music and choir.
Going up to Mt Rigi in the snow is pretty spectacular if you have a clear day. I've been to Rigi in the summer and in December, and December was breath-taking, above the clouds and tree line. On our day there were low clouds over the city, but the cogwheel train went through the clouds to fresh powdery snow and deep blue skies. The entire train gasped as we broke through the clouds.
Many folks here have shared their Christmas days in European countries, but I don't remember anyone talking about Switzerland, so this should be very interesting.
So glad you will be experiencing the Xmas markets. Safe travels!

Christmas Day is a Sunday this year,

On my Calendar Christmas Day is on a Monday this year.

It's a long while ago but I have spent 3 Christmases in Switzerland, near Interlaken. Around there the big Swiss Christmas meal and celebrations were on Christmas Eve night (including the exchange of gifts), culminating in Christmas Eve midnight mass (rather than midnight mass starting Christmas as in the UK). I was always surprised by how many shops and cafes/restaurants (not all, but enough) were open on Christmas Day, and how public transport was still operating to a not very modified timetable.

Things definitely did not totally close down as in the UK. And 26 December was a normal day for all intents and purposes.

Maybe that was unusual to that part of the country, and maybe things have changed since those days. Because of it's geographical position Basel may have different customs and practices.

Ooops- I did look at my calendar without my glasses. Thanks for the correction .🤓 So businesses could be closed Sunday, Monday, and Tuesday, December 24, 25, and 26. Thanks again for correcting my error.

any advice about restaurants open on Christmas Day in Basel?

Choose a few restaurants online and look at their website - I saw some that were open Dec. 24/25 but closed 26/27. Friends of ours in the restaurant business in the Berner Oberland are definitely open over Christmas - a very busy time!

December 26th is St Stephen's Day, a national holiday in almost all cantons.

Thanks so much for all your replies. You give me several ideas to consider. We will probably be staying in hotels since I thought the possibility of them having a restaurant that would be open is a good possibility.

Freiburg, Germany is not too far by train from Basel if you wanted to visit there. We once stayed at a resort in a village called Hinterzarten which was not too far from Freiburg and we rode the train from Freiburg to Basel and spent a day there. Freiburg is a nice city to visit during the time before Christmas Eve.