While Brussels technically includes 19 communes, or municipalities, most sights, hotels, and restaurants are clustered in the center in Stad Brussel (French: Ville de Bruxelles), the city's largest commune. Locals simply call this the centre, but the tours here distinguish a Lower Town and Upper Town. The Lower Town is physically lower, including the area around the Grand'Place and the Bourse. A steep slope leads to the Upper Town, around rue de la Régence, place Royale, and the Sablon squares. If you're arriving at Gare Centrale, an underground passageway links the lower concourse level directly with the Marché aux Herbes in the Lower Town, close to the Grand'Place.
Detailed maps of the Brussels public transportation network are available in most metro stations and at the Tourist Information Brussels in the Grand'Place. Get a map free with a Brussels Card (available at the tourist office or to download), which allows you free admission to around 40 museums, plus other discounts. Cards cost from €24, €32, and €39 for one, two, and three days respectively. A Brussels Card (Sightseeing) also gets you the above plus free transport on the hop-on, hop-off buses (€36 for one day; €48 for two days) or subway (€31.50 for one day; €46 for two days). Before deciding on a card, know that most museums are closed Monday.