Sibu Central Market is the town at full volume: vegetables from upriver farms, river fish, dried goods, poultry, fruit, and food stalls packed into one big, practical building. It is often described as one of Malaysia's largest indoor markets, and whether or not you care about the superlative, it feels satisfyingly busy.
Come in the morning, when the produce is freshest and breakfast stalls are doing brisk trade. It is a good place to try kompia or kampua mee before walking down to the waterfront.