Leave Brussels fast, and ride on red velvet seats to Cologne.
Return tickets are only £20 on the Belgian Railways Website (SNCB). Cologne is a great city: cheap, at £20 pp/pn in a 3-star hotel; excellent art galleries; and good beer.
Visit the Cantillon Brewery, near the Midi train station. This fine brewery produces gueuze, a sour and even sulphurous beer which is allowed to ferment spontaneously by contact with wild yeasts in the air. It's a love-it-or-hate-it thing - and you won't find out which it is for you unless you visit the brewery!
Use the Eurostar deal with Belgian Railways to travel on from Brussels at no extra cost.
Take the Luxembourg bound train to Libramont and then the bus number 8 to Bouillon on the River Semois. Stay at the Hotel Panorama overlooking river, town, castle and hills.
Listen to the town carillon play the Ode to Joy. The walking in the river valley and on wooded hills is wonderful and the food in the town is excellent. Return, if you can, on bus 45 to Bertrix for spectacular views of the Semois, tiny villages and the hills. Take the train from Bertrix to Libramont and then back to Brussels.
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