"Ithimid ag an gcúinne."
Translation:We eat at the corner.
Not with ag. What I assume it's talking about here is a restaurant at the corner of a square or something similar.
I agree but English also uses 'on the corner' which is my mind is interchangeable with at the corner when stating the location of something which I think 'ag' would cover here
At the corner would in my understanding mean something "close by", sort of this street and the crossing with the following street.