Belgium for me, too.
Nearer the time there will no doubt be a thread about getting there and back, but peeps might like to know - for planning purposes - that last time I took train to Dover, ferry to Dunkirk (which is France and not linked to the Belgian railway system), rode to De Panne (which is in Belgium and has a train station), then took train to Brussels for 9I think) about £25. There is some deal with tickets so you buy 10 at a time and have to use them within a year so if there were 10 of us we could do that. Then a five-minute ride to the cafe where we meet, and off we go. From the coast there is a tram that goes all the way along and for (I think) €5 and €3 for the bike you can get back to De Panne. Then a ride to Dunkirk and get the ferry, doze on ferry, and train home from Dover. I believe it is possible for the wealthy middle classes to buy a eurostar ticket to Brussels.