not a teacher
This is "nip" in the sense of "to go quickly, "to dart".
"I'm just nipping down/across/over to the shops to get some milk."
So, in your sentence it means making quick trips to Dublin.
This is a common usage in my region (Aust/NZ) and in British English. I'm not sure if it is heard at all in the US.
Student or Learner