In keeping with the theme - on horse or foot.

Foot. Horses are for the rich, and castle builders wouldn't have been rich. Well the head stone mason might have been special enough to ride the master's horse once in a while. A horse eats a lot of food (even on days when you don't use it!) Most people would have walked. Saddles were not near as advances these days. Wagons would have had terrible suspension (and the roads not very good) so even the wagon drivers would have walked. A human can walk farther in a day than a horse can. The horse can run fast with a heavy load, but otherwise isn't worth it.

Most likely they would have used oxen not a horse to haul the wagons.

You could rent a car out of Auxerre, but don't count on being able to get by in rural l'Yonne without one.

Haven't tried it, but it seems you could get, within 6 km, to Saint-Saveur-de-Puisaye - on bus 861 (need to call them) from Auxerre Saint-Gervais which is reachable by train from Paris.

I hitchhike all the time in France and it works great, locals are usually nice and I never wait more than 10 mins (but I’m french so IDK how it would work without the native language)

> (but I’m french so IDK how it would work without the native language)

You know exactly how that would most likely work out.

Customers from France have refused to talk to colleagues of mine because they're from Alsace. French people are not nice to others.

Not my experience but sorry to hear that

You could try BlaBlaCar

https://www.blablacar.co.uk/search?fn=Paris%2C%20France&tn=8...

I guess for the full medieval experience you walk?!