A place where a being is safe by the nature of the place, not by permission. Safety that does not have to be re-earned at the door.
Latin sanctuarium (a shrine, a holy place), from sanctus (sacred, made holy); the medieval sense of a place where a fugitive could not lawfully be seized is the sense kept here — safety belonging to the place, not granted person by person.
A place where a being is safe because of what the place itself is, not because permission was asked for and given at the door.