This small museum is built around Anton Chekhov's Sakhalin Island, the book he wrote after travelling across Siberia to study the penal colony in 1890. It is a harder, more revealing frame for the island than most tourist displays.
The collection includes editions of the book, material on Chekhov's journey, and literary exhibits. It is especially worthwhile if you want to understand why Sakhalin long sat in the Russian imagination as exile, edge, and punishment.