Sønderborg is 30km northeast of the German border crossing at Kruså, via Rte 8. It’s connected by trains to Kolding (162kr, 80 minutes) and the rest of Jutland.
The train station is on the western side of town, by the modern Alsion building. Town buses 1 and 2 connect the train station with the east-side bus station (on Jernbanegade, a block east of Perlegade).
The best website for planning travel is www.rejseplanen.dk.