Aalst's central square is a tight, irregular space ringed by guild houses, the Belfry, and the medieval Schepenhuis. The cafés along the edges keep terraces out year-round, and the square is host to a Saturday market that's been running for centuries.
It's also the natural starting point for any walk around the town: the church, the Beguinage, the riverfront, and most of the museums are within a few minutes' walk.