Brussels Midi has both luggage lockers and a staffed left luggage facility near the Eurostar check-in and Thalys reception. Both are open 24 hours a day, the staffed facility costs €4.00 per item per calendar day, the 3 sizes of lockers cost €3, €3.50, €4 per 24 hours.http://www.seat61.com/luggage-lockers-at-stations.htm#Left_luggage_in_Brussels