Christmas/New Years in Europe

Both 25th and 26th are public holidays in Germany, so you need to look at the websites for attractions you are interested in to check their opening times.
Hopefully, someone with local knowledge will be along to advise on restaurant openings etc.

Few cities in Germany catch my attention as does Nuremberg. I'm an architect and I love historic delimas and there is no better example that I am aware of than Nuremberg. Here is a good article https://www.nytimes.com/1984/04/08/travel/nuremberg-rebuilt-city-at-the-crossroads.html

When they say many close 24 - 26 Dec, it means that most markets finish up on the 23-24th, around the middle of the day. There are a few markets that are open after Christmas (google this, on Fodor's someone put together a good list), but by and large the purpose of these markets is over by the 24th as this is the main festival day in Germany (the evening particularly), and shops will be closed on 25 and 26 December. For the most part restaurants will be too, but if you are staying in a hotel with a restaurant, they may look after their own guests. You may find that museums and galleries open around the 26-27th, but by and large people in Germany are relaxing with family at this time. Trains are running to a holiday timetable, though, so if you think you'd want to see another picturesque town from the outside, you could hop a train to the next city and take your camera and snap facades if the weather plays along with your plans.

Lavandula

Here's a link to the majority of the Christmas markets in Europe. Note that most of them are ending 22-24 DEC. 25-26 is the German Christmas holiday. 28 DEC is a Sunday, and most everything will be closed, with exceptions in the major cities. 29 DEC is a Monday, and most museums will be closed, and some restaurants. 31 DEC is a German holiday, as is 1 JAN. That gives you two good days when you can plan on everything being open (27/30th).

https://www.brunnvalla.ch/christmasmarkets/germany.html

Each year when I begin reading about the issues of travel over the Christmas holidays, I find myslef grateful that I am here in Budapest. For the longest time I assumed that what went on here was typical but after reading so many of posts similar to this one that do a good job of reinforcing how little can be open in some societies, it means that planning a trip over the holidays can be tricky. You didnt mention Budapest so use this maybe as a guide to have ideas of what to look for in places like Nuremberg. I still put Nuremberg high up on the list if you can find things to do. I would love to spend a few weeks seeing how after WWII, accurately and faithfully they re-created the ambiance of the ancient city with almost nothing original remaining. I understand that Strasburg is pretty much the same but at a different scale. Facinating stuff this.

So, here is the list. See if the German cities have any of the same sorts of things going on and if they are open.

Dec 24 Christmas Markets
- The Christmas markets close about 2pm for the most part. But check
here for more information on the various markets:
https://community.ricksteves.com/travel-forum/hungary/budapest-christmas-markets-d26f8ab1-2048-4160-bfb3-bf13b096683e
Its last years information for the most part, but I dont exepct there
will be any significant changes.
- This is the slowest night of the year. No arguing that. But there are still things to do.

Dec 25 and Beyond Christmas Markets
- Those Markets that are open after Christmas (see the link above) will open about mid-day on the 25th. Some remain open until mid day on the 31st of December.

Other Activities
- Bathhouses (all days)
- Skating rink at City Park (all days)
- River Sightseeing Cruises (all days and evenings)
- Opera House (performances day and evening 25, 25, 26)
- Operett (performances 25 and 26)
- Sunset will be at about 4pm so it’s a great time to see the lights.
- The Great Synagogue and I presume the others worth visiting will be
closed the 25th but open the 26th until 2pm (Friday) and closed on
the 27th (Saturday)
- The 26th most of the commercial and tourist enterprises will be open.
- The 27th should be a normal tourist day with everything open.
- A list of whats open that I came across:
https://budapestchristmas.com/opening-hours

Random selection of Restaurants (plenty more but admittedly the better restaurants, not so much the mom and pop places)
OPEN 24, 25, 26, 31 DECEMBER
TwentySix https://twentysixbudapest.com/
KOLLÁZS – Brasserie & Bar https://www.kollazs.hu/
Spago by Wolfgang Puck https://spagobudapest.com/en/
Pest - Buda Bistro https://www.pest-buda.com/restaurant-in-the-buda-castle.html
Christmas Dinner Cruise https://budapestrivercruise.com/budapest-christmas-cruise
OPEN 25, 26 & 31 DECEMBER
Szeged Vendeglo https://www.szegedvendeglo.hu/
Callas Café https://callascafe.hu/
Sir Lancelot https://sirlancelot.hu/
Robinson https://www.robinsonrestaurant.hu/en
Dunacorso Étterem https://www.dunacorso.hu/

Look at larger cities, like Budapest and Vienna, for at least some Christmas Markets still operating during the last week of the year. The added advantage of the larger cities is that more will be going on besides the markets, more will be open, than in the smaller towns that are famous for Christmas Markets that really wind down Dec 23/24...save Strasbourg for a trip that places you there earlier in December.