Physical Fitness Challenges

I am doing the American Cancer Society biking challenge for August (300 miles). On track to exceed the number by the end of the month.

Having a challenge has really kept me accountable, and it has made me far more consistent in my routine and dedicated to fitness. I think I need something like it to keep me going.

Are there other challenges (charitable or otherwise) that keep you going or might help someone like me to self-motivate? My ordinary motivation level can be some weak-arse shite, and these really help.

Any suggestions appreciated.