For me it's the best city park ever.
Firstly it's the biggest one in europe located inside the city.
Secondly i had had great time in there. There is a lot place to play some team games, or just to lay down on the grass or sit on the bench.
I've been there with friend on bikes and it took us more than 3 hours to see whole park. And while exploring we had really good time! We've seen deer's really close. We almost got inside president palace (almost... :D ) By foot it took me about 1,5h to walk though the park in straight line.
So if you have a chance to go there, you must do it! :D

PHOENIX PARK Dublin can be a pretty hectic city despite its size and pretty expensive too. So if you visit in summer and need a day to relax, I recommend you do so in Phoenix park. For familys, theres a zoological garden but if you really want to relax, this is the quietest and most layed back place to do so. Stroll, watch a crickett or football game, have a lunch in one of the scenic tea rooms, see the Wellington monument or just sun bathe on any of the rolling greens. Peace in the heart of the city

Phoenix Park is one of the biggest parks in Europe and I think that Phoenix Park is the right place to go for a picnic a romantic walk or just for a great run- I went for run maybe 3 times ;)
I love the Dublin zoo too!

Forget that you are in the biggest city in a Republic! Loose yourself! Explore! Be a scout or a little kid again! Or just roam the broad green oasis!

Nice place for a stroll in the woods and escape from the city for an hour. Easy hike from Temple bar via ha'penny bridge