GB wasn't specified so there is the boring Bangor to Bangor. Further afield is a doddle. E.g.
Dietikon to Dietlikon (train continues to Pfäffikon and Wetzlikon)
Nyköping-Linköping-Norrköping-Jönköping
Ketegyzhaza to Lököshaza is one stop
If we're including Ireland, York to Cork.