Hi, Steven. I was wondering about the borders between the kingdoms, or even local lords. Would a traveler be able to journey the length of Westeros unchallenged, or would they have to check in with the different lords whose lands they passed through?

It depends. By and large, there seems to be freedom of movement across the countryside – no internal customs barriers (and back in the day they were actual barriers), no checkpoints or toll-roads, etc. However, entry or exit from a city or walled town or holdfast is in the control of the lord of that town.