Just got a notification from Apple that they are offering an Activity achievement on Saturday, which is Earth Day. To get it, you need to get 30 minutes of outdoor exercise with your Apple Watch. This unlocks a badge in Activity, as well as some special iMessage graphics.
I think this marks the third such challenge they’ve offered, with the first two being Thanksgiving (5k of walking) and January/NewYear ( a full week meeting your move goal in January).
Macrumors, AppleInsider, and other Apple news sites have more details.
I wish they would step up these rewards. Gamification is really helpful, and Apple hasn’t taken advantage of it to the extent that Nike and other vendors have.