I have dust mite allergy ! and i want to go out of town ! which better for my allergy cold city or beach ?

Beach: The beach would likely be better. Dust mites tend to accumulate more in the winter due to the closing of the windows and poorer circulation. To prepare you for your trip, i would discuss therapy options with your allergist/immunologist to make sure that you have minimal symptoms on your trip. If you have not seen an allergist, i would recommend seeing one to confirm your allergies.