Q. Can I carry items in a park inside a city that has an eiruv on Shabbos? Does it make a difference how big the park is? If it is surrounded by a fence and has gates? If it has benches, many trees or water fountains?

A. Poskim (Chelkas Yaakov1: 201, Orchois Chaim 358, 10-11, Shemiras Shabbos Kehilchoso N.E. 17: 118) maintain that if there is an eiruv that surrounds the city, you may carry on the parks included in the eiruv area. The above applies, even if they are larger than an area of beis sossaim (5000 sq. amos or approximately 1250 sq. meters) and could be considered the karfaf that our Sages banned carrying an object within, when it was dedicated for non-habitation purposes, and was not initially walled as part of a residence. (eino hukaf ledira).
The reason these Poskim permit is that parks are land that was set aside for public use, and is maintained for recreational and ornamental purposes. A public park is frequented by the public who sit on the benches, play on the grass or enjoy the walk and the view, therefore it would be considered hukaf ledirah. (See Chazon Ish Maasros 5: 8. Orchois Chaim ibid. quotes Poskim that disagree)
Although Shulchan Aruch (O.H. 358:1) rules that gardens and orchards are not considered hukaf ledirah. it refers to gardens and orchards that are fenced to protect their fruit and not for public use.
Biur Halachah (ibid.) explains why a “dir” used for protecting animals is considered hukaf ledirah more than gardens and orchards. See Noda Beyehuda (2: 47), and Maase Oreg p. 137 on carrying in a Zoo. Imrei Yosher (2: 80) quoting Beis Meir.
Horav Shlomo Miller’s Shlit’a opinion is to be lenient for the ones who in general use an eiruv. It is also a widely accepted view today. The Rov added that although some large parks, have areas that people cannot walk on them because of the planted flowers, flora or the thickness of the shrubs, since they are kept for ornamental and decorative purposes, they are not considered not hukaf ledirah and therefore permitted. Being fenced or not, does not in this case make much of a difference, once they are included in the city eiruv.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a