There is an island named Graff where knights and knaves live.
Knights always speak the truth; knaves always speak lies.
You ask 4 people (at the same location) where the castle is, and they reply:
Alex: "The castle is North of here. Jim is a knave."
Jeff: "The castle is West of here. Jim is a knight."
Jim: "The castle is East of here. Jeff is a knight."
Alice: "The castle is South of here. Alex is a knave."
In which direction is the castle?