Can I use a Eurail Benelux Pass to go from Brussels to Arras France and return? Or is the pass only valid within the borders of the Benelux countries? Therefore I would have to buy a separate ticket to go from Brussels to Arras, and the return? Thanks in advance for any help.
Or is the pass only valid within the borders of the Benelux countries?
Yes, only valid in Benelux countries. You can buy a ticket that includes the French portion only and use the pass for the Belgian portion.
The real question is: "Is it a good value to buy a Benelux Pass when train prices are relatively inexpensive? If you want to use the Thalys express trains with the pass, there is a mandatory seat reservation fee that is fairly expensive.
bbergos, are you over 65 by any chance? Extra bonus on Belgian trains if so...