This is a regular add-on deal which allows me to travel to any Belgian station.
First I get the train to Brussels as usual.
Then I'm allowed one extra leg to any Belgian station.
» An Any Belgian Station ticket covers travel all the way from the UK to anywhere in Belgium and back.
» You travel with Eurostar to Brussels-Midi, then it’s a simple change to an SNCB train to continue your journey through Belgium.
» High speed Thalys and ICE trains, as well as the Brussels Metro and trams aren’t covered by your ticket.
» You won’t have a seat booked on the local train, so just hop on and find a seat.
The great thing is I didn't have to specify which Belgian station in advance...
(and I've never been to any ofthe others)
...which begs the question...