Any activity which contributes to wellbeing can count as part of Challenge 2. 
You might start walking more, use an outdoor gym or maybe take part in a yoga session. 
Get out on your bike and enjoy the countryside or go for a swim at the local pool.
Physical challenges can also be singing or taking part in a performance (if you are in Wear Valley you might consider taking part in our Empire summer activity - 'Pants to Panto') and, of course, if you are litter picking for Challenge 1 you are also taking part in Challenge 2!