The borders between Scotland, England, and Wales are effectively like state borders in the US. Unless you see a street sign, you wouldn't know you crossed it.
NI is physically on a different island, so requires a boat or plane ride.
And all of the UK (ignoring the territories and ex-colonies) is on islands. And require a valid passport, passing through customs/immigration checks, and either a plane, boat, or train ride.
The borders between Scotland, England, and Wales are effectively like state borders in the US. Unless you see a street sign, you wouldn't know you crossed it.
NI is physically on a different island, so requires a boat or plane ride.
And all of the UK (ignoring the territories and ex-colonies) is on islands. And require a valid passport, passing through customs/immigration checks, and either a plane, boat, or train ride.