I've heard people complain that Brussels is "boring," but I beg to differ. Sure, there are lots of government offices, but there are also fascinating museums, beautiful buildings and more than all of that--an incredible food scene.
I've never had a bad meal in Brussels. I've also never had a bad snack in Brussels. Or a bad dessert. I've got a secret plan for how and what I eat when I'm there. Here's how it goes.
Start with frites in the late afternoon. There are plenty of stands and restaurants selling french fries near the Grand Place. My favorite is a place called Fritland. They pretty much only sell fries, but they have about eleventy-hundred different sauces, aoilis and ketchups to go along with them. (Okay. Eleventy-hundred might be an exaggeration.) But those frites are no joke--they're easily the best fries I've ever had.
After eating a cardboard funnel full of fries, you're probably not going to immediately be hungry again, so you shouldn't plan on dinner until a little later. You could maybe go to the brewer's museum, which is right on the square. It really isn't much of a museum, but admission comes with a sample draught of Belgian beer. Or, just find a nearby pub and have a beer there.
When you're finally ready to eat again there are plenty of options for good, authentic Belgian cuisine nearby. Scope out some of the restaurants, and find a place that looks crowded. Even though it seems like it's very touristy--with hosts standing outside the front door, trying to entice travelers to come inside--the food at those places is the real deal. I've been taken to some of those restaurants by locals, in fact. Order mussels, or maybe beef carbonnade (an incredible stew made with beef, onions, Belgian beer, and prunes).
Here's the best part of your eating strategy, though. Rather than having dessert in the restaurant (which almost certainly would be delicious), you're going to head back out to the Grand Place. In the area around the square, there are lots of chocolatiers. I visit all of them. Just make the rounds. Walk into the shop, and ask the clerk for a single piece of chocolate--I let the clerk choose his or her favorite most of the time. I buy that single piece, eat it, and then move on to the next shop, where I let the next clerk pick out a single piece of chocolate for me to sample. Godiva, Neuhaus, Leonidas, Galler (my personal favorite), and other chocolatiers are all right there. Maybe it's a little excessive to eat 8-10 pieces of chocolate for dessert, but since you're eating them one at a time (and walking to the next shop in between), it doesn't feel inappropriate, at all!