Some high-speed trains require seat reservations, mainly in France, Spain, Italy + cross-border routes such as Eurostar and Thalys. You need to choose which one you'd like to take in advance. Eurostar and Thalys have a limited quota so you need to book well in advance (can sell out weeks prior). Check availability here : https://www.b-europe.com/EN/Booking/Pass#TravelWish

Eurostar to Lille or Brussels (30€)

Then there are dozens of reservation-free trains from Lille or Brussels to Bruges, simply board the one you'd like (and add it to the app before boarding). Same practice in most of Europe :)

- Thalys Brussels - Paris 27€ (can sell out well in advance)

- TGVs in France : limited 10€, then 20€ until the train is full. Check here : https://travel.b-europe.com/Eurail-GE/en/booking-tgv#TravelWish

Alternative : reservation-free regional trains

Use bahn.de for planning your itinerary, very reliable tool

Sorry for the delay in replying.  Thank you very much.  Finally on my way.  Inc now are Prague and Austria :)