From Sydenham train to Belfast Central Train Station then train to Dundalk Train Station. 2 h 20 min 26€. From Sydenham train to Belfast Europa Bus Centre, bus to Newry, Newry Bus Station, then line 160 bus to Dundalk, Dundalk Bus Station Long Walk. 3 h 6 min 32€. From Belfast City Airport (BHD) drive to Dundalk. 1 h 12€.