There are engineering works planned on the Dutch network that weekend.

Trains are likely to run but on an altered timetable (20-30 min longer). Check back in a few weeks. :)

Thanks so much. Super helpful and will check again closer to the date. 

Supposing you mean seat reservations instead of tickets, then the best place to book is www.raileurope.com. Regular tickets can be booked ok eurostar.com.

It looks like there is still no availability that weekend. Maybe I am best off to book a flight instead.

It looks like Eurostar won't be running to Amsterdam that weekend because of engineering works in Belgium. They will run Brussels-Paris (book on raileurope.com) though and you can use other trains (no reservations needed) to get from Amsterdam to Brussels.

I would definitely not fly! Very expensive (while you have a train pass!), stressful and more importantly slower.

Since Eurostar is expensive and availability to Brussels could be limited (thanks to their annoying passholder quota), let me suggest this alternative:

- TGV Paris-Nord - Lille-Flandres 08:42 - 09:48 10€ on top of your pass (available from 22nd January)

- IC Lille-Flandres - Kortrijk - Antwerpen-C. 10:09 - 12:23

- EC Antwerpen-Centraal - Amsterdam Zuid 12:29 - 13:48

- subway to your final destination