Tresoar — Frisian for "treasure" — is the regional archive, library, and literature centre. The reading room is open to the public, and the exhibition gallery on the ground floor mounts changing shows drawn from the collection: medieval manuscripts, photographs of the great floods, Frisian-language printed books, maritime charts.
For anyone with even glancing interest in Frisian history or language, an hour here adds a great deal of context to the rest of the city. The centre also runs guided tours and lectures; ask at the desk.