There is an orienteering race taking place on danube island. No matter if you are a beginner or pro, everyone can attend. All you need to bring is 6 euro starting fee (if you are a group you can split the costs). Also perfect for just walking/hiking if you don't like to run ;)
We'll meet at 2:30 at U2 subway stop "Donaustadtbrücke". If you want to start later, it's possible to start till 5pm...
any more questions?