[Closed] Suggest a challenge?

I'm looking for ideas for a mountain bike related challenge. Maybe something to do for charity but mainly something to test me and any mates that come too.

I usually ride twice a week and have enjoyed the odd enduro. I wondered about a 24 hour event or some sort of long distance off road trek? But I have little idea which event or route would be 'best'. Would love to hear your ideas/suggestions!

Cheers,