Perfectly and properly Palladian, this mansion was first built in 1616 and remodeled by Robert Adam in 1764. Adam refaced most of the exterior and added the gaudy library, which, with its curved painted ceiling, rather garish coloring, and gilded detailing, is the sole highlight of the house for decorative arts and interior buffs. What is unmissable here is the Iveagh Bequest, a collection of paintings that the Earl of Iveagh gave the nation in 1927, starring a wonderful Rembrandt self-portrait and works by Reynolds, Van Dyck, Hals, Gainsborough, and Turner. Top billing goes to Vermeer's Guitar Player, one of the most beautiful paintings in the world. In front of the house, a graceful lawn slopes down to a little lake crossed by a trompe-l'oeil bridge -- all in perfect 18th-century upper-class taste. The rest of the grounds are skirted by Hampstead Heath. Nowadays the lake is dominated by its concert bowl, which stages a summer series of orchestral concerts, including an annual performance of Handel's Music for the Royal Fireworks, complete with fireworks. A popular café, the Brew House, is part of the old coach house, and has outdoor tables in the courtyard and terraced garden. COST: Free. Tube: Golders Green, then Bus 210.