The Mt. Shasta Sisson Museum is the town's best compact introduction to the mountain and the communities around it. Exhibits cover local history, railroads, water, geology, forests, and the practical life of a high-country town that sits under one of California's most recognisable peaks.
It works well at the start of a Mount Shasta visit, before trailheads and viewpoints blur together. The museum is modest, but the context helps: you leave with a better sense of why the mountain has drawn loggers, climbers, spiritual seekers, scientists, and road-trippers for very different reasons.