The Portsmouth Athenæum is a private membership library and museum that has been operating from its Market Square building for over two centuries. Its collection of more than 50,000 volumes includes rare books, manuscripts, and a research archive on New Hampshire and New England history. The reading room — panelled, high-ceilinged, lit by tall windows — is one of the most beautiful in the region.
Non-members can visit the gallery on the ground floor, which hosts changing exhibitions drawn from the permanent collection and external loans. The subject matter typically focuses on Portsmouth's maritime, colonial, and literary history. The building itself is worth a stop — it faces directly onto Market Square and its Federal facade is one of the anchors of the historic streetscape.