The Patan Museum, housed in the restored west wing of Patan's old royal palace, is widely considered the finest museum of Nepalese art in existence — a world-class collection of Hindu and Buddhist bronze sculpture, decorative arts, and religious objects, presented in beautifully restored Malla-period rooms with excellent contextual information. It is the single best introduction to the art and religious culture of the Kathmandu Valley.
Technically in Patan (Lalitpur) rather than Kathmandu, it is about 20 minutes south of the city centre. The collection's strength is the metalwork — the bronzes here represent the apex of Newar artistic achievement, objects that influenced Buddhist art across the Himalayan world. The courtyard setting is also architecturally exceptional. Allow two to three hours.