The Museum of Northeastern Isan Culture sits on the original downtown campus of Mahasarakham University, in a quiet group of buildings under big trees a few minutes' walk from the city's central streets. The collection is small but well-organised: rooms on Isan textiles (mudmee silk and cotton), on the Buddhist and animist rituals of the village calendar, on the Lao-Isan language and the mor lam musical tradition, and on archaeological finds from the prehistoric and Dvaravati periods of the upper Mekong basin.
This is the best single hour for understanding why Isan feels different from the rest of Thailand. The captions are in Thai with patchy English, but the displays are mostly visual, and the staff are friendly and used to academic visitors. Entry is free or nominal. Combine it with a walk along the campus boundary to the food stalls that open in the late afternoon outside the main university gate.