Frisk gets lost in the forbidden forest and the Big Bad Wolf starts tormenting them till Fairy Goat Mother saves them! Beyond the forest is the Kingdom of Ebott where the monsters live. King Asgore rules over them and the Knights of the Round Table keep everything at peace.
I’d imagine that Sans as Lancelot from the Knights of the Round (Not cause he has an affair with Guinevere nOT AT ALL)
He’d probably never reveal himself as a knight unless Frisk does a Genocide run lol.