Car rental in Brussels

Best mode of transport between cities here is usually the train. But the train connection between Dunkirk and Bruges is a difficult one, so a car is not a bad idea in this case. You can drive from Brussels first to Dunkirk and drop off in Bruges, taking the train back after overnighting there, so avoiding the traffic jams around and driving through Brussels.

Or to avoid the busy traffic in and around Brussels you can take the train to Bruges and rent the car there (and bring it back) for the 1 hour drive to Dunkirk. Train back from Bruges to Brussels the next day. Maybe not the cheapest option but needing the least amount of time to my opinion.

For time tables and tickets you can use: http://www.belgianrail.be/
Under the “International Travel” button you can find the trains for Dunkirk.

I've picked up a car in Brussels at Gare du Midi/Zuid Station, driven around Belgium, and dropped it off in Bruges, and it isn't too difficult. It's smart to look at Google Street View to get an good idea of the easiest way to get out of the city. Warning--depending on your destination, there's a long tunnel as you leave Brussels and your GPS or map app won't work in it--so be sure you know where you want to go before you enter it. In the middle the tunnel divides and it isn't well-signed, so at the last minute I had to guess which exit to take.

If your travels take you near the ferry port in Dunkirk, can I suggest that you be very sure that you keep your doors locked and be very alert. This includes on the A16 motorway.

I normally am able to keep out of the Calais problems with economic migrants illegally entering the UK by breaking into trucks and stowing away, and there was a big lull after the camps were bulldozed and the people were relocated hundreds of kilometers away elsewhere in France to special camps. But they have been filtering back and have often become quite violent to achieve their goals including putting trees and cables across the roads to stop the trucks so they can force their way in. This affects other traffic on the roads, and the Dunkirk crossing is now often their route of choice since the security is so tight around the Channel Tunnel and the Calais Ferry Port.

I have seen people running and walking across the A16, and when I have stopped for a meal in Dunkirk seen large numbers - 10 or 20 - moving down the roads towards the truck parks for the ferries in Dunkirk.

It was enough to make me uncomfortable, but I have never been personally affected except by having to put the brakes on hard to avoid running into somebody walking across the motorway.

This is why as you approach Dunkirk you will notice that the speed limits have been reduced and there may be electronic signs warning of items in the road.

Forewarned is forearmed.

I hope you find what you are looking for in Dunkirk.

Thank you for you helpful responses!

Note that there may be a dropoff charge for return in a different country, i.e. Amsterdam. I would rent and return in Bruges, because the highway traffic in that part of Belgium can be very bad on weekdays. There is no good reason to drive from Brussels to Bruges. As noted by others, trains are cheap, fast, and unreserved for Belgian tourism. Unless you plan to make "car" stops on the way to Amsterdam (for example, the Delta floodworks, Keukenhof (in season), or Aalsmeer flower auction, I would train from Antwerp (nice city) or Brussels to Amsterdam. Utrecht, Den Haag/Delft, Leiden, Haarlem are easy train daytrips from Amsterdam. Den Haag or Leiden could be an overnight. The windmill places can be seen by car or by public transportation, easier by car. Turn on GPS "Avoid Ferries", in my opinion, for that.