Mackay is a working tropical city on the Pioneer River, halfway between the resort pull of the Whitsundays and the mining roads inland. It is often treated as a gateway, but the city itself has enough riverfront, public art, gardens, and old Queensland streetscape to make a spare day worthwhile.
The best way to read Mackay is along the Bluewater Trail, which links the river, lagoon, public art, and city edges. Artspace Mackay gives the centre a real cultural stop, while Mackay Regional Botanic Gardens shows the local dry-tropics flora better than a generic city park.
Do not add Mackay to a Queensland trip expecting Airlie Beach. The beaches and reef access are better elsewhere. Come if you want a grounded sugar-and-port city, a softer pause on the Bruce Highway, or a base before heading inland to Eungella and the Pioneer Valley.