Khon Kaen National Museum is the city's best cultural stop, with archaeology and art from the wider northeast. It is especially useful for understanding Dvaravati and Khmer-period finds from Isan, which can otherwise feel scattered across temple sites and provincial towns.
The museum is not flashy, but it fills in the historical depth behind the region. Go before visiting sites farther out in the province, or use it as a cool midday break from the heat.