hi there,
The
Retiro Park is a nice place to be for outdoor activities but my absolute favorite place for outdoor activities in Madrid is at the
Casa de Campo Park.
You can get there very easily on Madrid's metro and things you can do there include visiting the Zoo Aquarium de Madrid and the nearby amusement park called Parque de Atracciones, where you can enjoy high speed rides and water rides.
Hope this helps
Vacationbuddy