The 1881 Courthouse Museum is the best in-town stop for making sense of Custer's early years. The building itself matters: it was Custer County's courthouse when mining camps, ranches, stage roads, and new towns were still sorting themselves into something permanent.
Inside, the exhibits cover local history rather than trying to tell the whole story of the West. Expect mining tools, courtroom material, family objects, and displays on life in the southern Black Hills. It is small, but it gives useful texture before you head back out to the roads and parks.