Henry the Hundred Miler

I've been thinking about riding hours and kit because that's the bit I don't know anything about and need the most help with.  Meeting my friend Henry for lunch yesterday made me think I need to start training for what is essentially an endurance race...

Me: "what did you do at the weekend, Henry?"

Henry: "oh, ran 100 miles."

Henry's advice was: start running and try crossfit. I'm off! Don't even know what crossfit is!

Have you tried crossfit? Would you recommend it?