Caher Island sits in Clew Bay, a small and largely forgotten place except among those who know it as a site of early Christian pilgrimage, associated with the cult of St Patrick. That an ancient road or trackway should survive there at all is quietly remarkable: most islands of this size and remoteness have lost any trace of organised movement across their surface, yet here the ground still carries the outline of a route, a record of repeated passage by people who had reason to cross the island with enough regularity to leave a mark.