The de Young is San Francisco's premier fine arts museum, with collections spanning American painting from the colonial era to the present, plus strong holdings in African, Oceanic, and textile art. The building itself, designed by Herzog and de Meuron and opened in 2005, is clad in copper panels that are slowly oxidizing to match the green of the surrounding park.
The best-kept secret is the Hamon Observation Tower -- a 144-foot tower with 360-degree views of the park, the ocean, the Golden Gate Bridge, and the city skyline. The tower is free, even without museum admission. Take the elevator up on a clear afternoon and you will see why Golden Gate Park was worth building.