Danish Railways (DSB) operates a train from Tønder to Flensburg hourly. Tickets cost $10 - $15 and the journey takes 24 min. 4 other operators also service this route.
How to get from Tønder to Flensburg
From Tønder Busstation line 116 bus to Tinglev st then train to Flensburg. 1 h 51 min 108 kr. From Toender st train to Niebüll, train to Husum, train to Jübek, then train to Flensburg. 2 h 38 min 271 kr. From Tønder drive to Flensburg. 48 min 52 kr.