The 10-year old son will have, by far, the BEST "How I spent my summer holidays" essay, report, or narrative story when he returns to school in September... When I was about that age, one of the first things teachers usually did to get children back into a school frame of mind was to have them each write an essay describing what they had done over their holidays. The best one or two usually were read aloud.
I always disliked when other kids had better accounts of what they did, where they went, or the places they saw over summer school holidays. NOW he gets to trump all their stories with tales of knights, castles, pilgrims, meeting people from all over the world, and the sheer adventure of it all.
My advice is to take lots of photos to PROVE he actually did all these very, very cool things...for a 10-year old. Without photos, some adults simply will not believe.
Go for it!