Here’s the walk Daniel at the Renaissance Hotel mapped out for me, with small additions by me. Going to the center of town without stopping would take you 25 minutes. A leisurely round trip will take you two to three hours. For those not staying where I began, pick this up at any point (logical ones would be the Grand Place or the Palais Royal).
Begin at the Renaissance Hotel or the Brussels Luxemburg Station. Travel east, away from the station toward the center of the city on the rue du Luxembourg. You’ll pass through the Square de Meeûs, which was quite pretty in the spring. Practical note: There’s a GB Express supermarket here right before you get to the avenue des Arts, part of the ring of roads round the city center. It’s the only place to pick up food I saw.
You’re at the edge of the Royal Quarter. Pass the Avenue des Arts and walk right up the rue Ducale. Turn left on the place du Palais. The Royal Palace is on your left, its gardens are to your right. They are filled with joggers. Side note: Belgian men are very good looking, like everything else in the country an interesting mix of Flemish and French. Go in and stroll around among the fountains for eye candy.
When you’re done, continue to the place Royale and turn left on the rue du Régence. You’re traveling downhill, passing government ministerial buildings on both sides. The street is not perfectly straight, either. After about ¼ of a mile you will come to a gem of a gothic church on the left, Nôtre Dame du Sablon. It’s from the 14th and 15th century with magnificent, colorful windows and intimate in size. Go in and look around.
When you leave the church you are at the Place du Petit-Sablon. There is a small park here filled with statuary of Belgian heroes (several killed in the conflicts between the United Provinces that became the Netherlands and Spain in the 16th century) and blue flowers and orange tulips. This is a lovely pause either now or on the return.
Turn right toward the place du Grand Sablon, filled with fashionable shops and restaurants. At the end of the place, you will see the Cathedral on your left. Head towards it (alas, it was not open when I got there.). From the cathedral, walk right towards the center of town up the boulevard des Empereurs. You should see a small medieval tower on the same side of the street. This is the corner tower of the first wall built around the medieval city of Brussels. It’s from the 12th century and also housed prisoners. Fittingly for Europe, where history is simply part of the fabric of a city, it’s right next to a bowling alley.
Continue on the road and turn left at rue de l’Hôpital. This turns into the rue de la Violette. You’ll see the back of the Town Hall (the white Gothic structure) on your right after about two-three blocks. Head towards it. You’re in the Grand Place!
The Grand Place was one of the few places I saw that fully lived up to its reputation. The medieval buildings on one side were destroyed in a French shelling in the late 1690s, and the buildings are from directly after, all gilt High Baroque. The medieval town hall survives, but looks like it was restored in the late 19th century by the sort of restorers who liked to "improve" as they restored. It’s bristling with statues and quite magnificent.
This is where my walk ended. The Bourse and the Mannekin-Pis are a block away, and I admit I skipped the Mannekin-Pis deliberately. I traveled back to the hotel the same way, but enterprising walkers could add on the European Parliament district and the Art and history museums by walking a little farthe along the avenue des Arts and heading out the rue Belliard instead of the rue du Luxembourg or could head in the other direction down the peripheral boulevards to the Avenue Louise.