The California Academy of Sciences packs an aquarium, a planetarium, a four-storey rainforest dome, and a natural history museum under one spectacular living roof. Renzo Piano's 2008 building is itself a marvel -- the undulating green roof is planted with 1.7 million California native plants and modeled on the city's hills, and a central glass atrium opens automatically to ventilate the building.
Inside, you can walk through a glass tunnel surrounded by reef fish, ride an elevator into the canopy of a simulated Amazonian rainforest, and watch a digital star show in the Morrison Planetarium's 90-foot dome. Thursday evenings (21+) feature cocktails, DJs, and access to all the exhibits in a more grown-up atmosphere. It is one of the best science museums in the country and easily a half-day visit.