Hi Basilio,
Welcome to our community. How nice it is that you are coming to Dublin soon!
From personal experience, I can recommend the Howth Cliffs. They are just 30 minutes by DART from the city center (the coastal/suburban train) and offer stunning views of the Howth Peninsula. You can easily reach the start of the Howth Cliff Path trail from Howth Dart Station.
Here's some more info on
Dublin's Coastal towns, including Howth. Since you plan to be in Dublin for a few days, I'd recommend using a
Leap Visitor Card to move around (it includes the Dart Train to visit Howth and is quite affordable).
You could alternatively take a day trip to the Cliffs of Moher with a
tour operator, but it would be a longer drive and take the entire day. Some like Wild Rover or
Paddywagon offer this type of day trip.
Do you already have other things planned in Dublin? Let us know if you want further recommendations to fill the rest of your time here.
Talk soon and let us know how the planning goes!
Antoine