What's the must-see thing in Brussels?

Grand-Place. Not the Atomium, not Manneken Pis. The medieval square sits at the center of Brussels' pentagon, the 1.5-kilometre-wide ring road that traces where the city walls stood. French artillery under Louis XIV reduced the original buildings to rubble in 1695, and what you see now went up in the five years after. Each guild funded its own facade and competed with its neighbors. The result is roughly 40 ornate fronts pressed together around a cobblestone rectangle. The gold leaf on the Maison du Roi catches afternoon sun around 4pm and turns a warm amber that photographs consistently fail to reproduce. At night the city projects colored light shows onto the facades every 30 minutes from dusk. Morning is better for a first visit. Before 9am you might have the square nearly to yourself. The smell of fresh waffles from the shops on Rue Charles Buls reaches you before you see the storefronts.

The Royal Museums of Fine Arts of Belgium sit on Rue de la Régence, about a 10-minute walk uphill from Grand-Place through the Mont des Arts gardens. The institution dates to 1801 and holds over 20,000 works. The Old Masters wing is the draw for first-timers. It has one of the strongest concentrations of Flemish painting anywhere, with multiple Bruegels and a Rubens collection that fills several rooms. The connected Magritte Museum opened in 2009 and spans five levels with around 230 works by the Belgian surrealist. A combined ticket currently runs €15. Allow 2-3 hours for both wings. The underground Magritte galleries stay cool even in July, which makes this a good afternoon choice when the temperature outside reaches 28°C.

The Atomium stands in Heysel park, about 6 kilometres northwest of the city center. André Waterkeyn designed it for the 1958 World's Fair as an iron crystal magnified 165 billion times, and it rises 102 metres. The top sphere has a viewing platform. On clear days the flat Belgian countryside is visible for roughly 45 kilometres in every direction. Tickets run €16 for adults, and booking online tends to save 30-45 minutes of waiting on summer weekends. The interior feels like a 1960s space station. Curved steel corridors connect the nine spheres via escalators, and every footstep echoes off the metal walls. From 102 metres, the medieval pentagon of central Brussels is visible to the south and Brussels Airport at Zaventem sits 12 kilometres to the northeast.

A note on Manneken Pis, because everyone asks. The bronze fountain on Rue de l'Étuve dates to 1619 and stands 61 centimetres tall. It is tiny. You will see it, take a photo, and move on within 90 seconds. Worth a detour if you're walking from Grand-Place to the Marolles flea market on Place du Jeu de Balle, which runs daily until 2pm. Not worth a special trip. If you have a fourth hour in Brussels, spend it at the Cathedral of St. Michael and St. Gudula on Place Sainte-Gudule instead. Construction started in 1226, the twin towers took another 300 years to finish, and the stained glass in the transept throws colored light across the limestone floor around 10am. Entry is free.