A lot of manifold Christmas Markets open every year in Northern Germany.
An overview of all larger Christmas Markets 2025 travelers is provided by public regional TV and radio station NDR in German language. The sub-pages are sorted by federal state, large cities and the very special category Christmas Markets on mansion estates (Gutshöfe) - a tip for travelers searching experience off the beaten tourist path.
Here you can find an overview for Bremen and Bremerhaven - provided by public Radio Bremen.
For best translation I recommend DeepL.
Good Christmas travels for everyone.