Ich bedaure sehr, dass ich dir keine erfreulicheren Informationen geben kann aber hier hab ich zusammengefasst, welche Möglichkeiten es dennoch gibt.
It is magnificent to hear that you'll be spending the festive period here with us on the Emerald Isle. There are a couple of options that are available to you, but they are quite limited. Firstly, if possible, depending on your schedule, you could take a late bus on the 24th December from Dublin to Belfast. This route is available with Bus Eireann
Furthermore, you've mentioned that you don't own a car. Are you perhaps able to drive? There is the option of renting a vehicle whilst in Ireland, this can be done in Dublin, and you can travel to Belfast. It's possible to leave the car in Belfast, depending on the rental company you decide to choose. We have lots of helpful information
and the ability to search for a rental company within our rental section.
Thanks everyone for the suggestion. Regarding Aircoach, please double check as on their website it seems that they do not have services on your travel dates
. I would love to hear more about your plans and what you hope to get up to in Belfast city.