B243 - newly built goes from the A7 down to Osterode and then leading to Nordhausen, giving you a straight connection east to west in the southern part.
B4 from Nordhausen leads to the B242 which crosses the Harz via Torfhaus to Goslar.
B6 and B6N are newly built and connecting the East and west in the northern part.
When traveling by car from the Netherlands, France, Belgium you need to head to the A7, which is a motorway that connects the South and North of Germany. You will pass Kassel and then take direction to Hannover. Depending on which part of the Harz you heading to, take exits between 66 and 72.
Look for more details in the town's information page.
Trains go to 20 major towns in Harz.
A great way to get around Harz is the Narrow Gauge Train, these services run from Wernigerode to Brocken or Nordhausen, and Quedlinburg to Nordhausen and Hasselfelde Check out their link:
You can get direct trains from Berlin to Wernigerode and Quedlinburg, tickets can be as little as 15 Euros one way, check out the website for term and conditions:
In the south check out
TIP: The HarzTourCard enables you to travel by bus, train and narrow gauge train as much as you like within three days. It cost from 18 Euros. Check out www.insa.de or the local tourist information.