Yes you can. As a member of a recognised walking club, you enjoy a €1.5 discount per walk. If you walk for 2 days, you get 2 x €1.5 = €3 discount.
If you are a maximum of 12 years old or you walk as a group with your youth movement, you will enjoy a special concessionary rate of €5 per walk, regardless of the distance. However, you no longer get a club discount on this.