Town Museum 't Gasthuys occupies the site of Aalst's old hospital and tells the city's story through archaeology, local history, temporary exhibitions, and displays on Aalst Carnival. The building gives the museum extra weight, since the old wards and hospital spaces are part of the visit.
It is the best single stop for understanding Aalst beyond the market square. The carnival material is especially useful if you are not in town during the event itself but still want to understand why it matters locally.