Belgium has 5 ports
able to receive yachts:
1) Antwerp - for Antwerp you have to enter the "Westerschelde" a very busy waterway since it is the main entrance to the large port of Antwerp.
You have to watch not only the traffic but also the regular shipping
lane since this estuary is full of sandbanks. Best is to travel at daylight if you are not familiar. Just at the beginning there is the small port of Breskens with an excellent marina.
The seaports of Belgium are: 1) Zeebrugge - Zeebrugge is a very busy harbour with many ferries leaving for the UK. Make sure that you are familiar with the approach.
Same for Oostende. Make yourself familiar with the approach.
Between Osstende and Zeebrugge you have Blankenberge. Blankenberge has an issue with the entrance of the port which is often, when not dredged, no more than 1.40 - 1.60 at ebbtide: enter only at HW if you sport a deep keel
The last one is Nieuwpoort which got a large marina but is the least attractive (in my opinion). The Belgian ports
are at close call, no more than 20 nm away from each other.