This is a photo of the Catavento ("Pinwheel") Museum in São Paulo. It is probably my second favorite after Butantan (the snake and spider museum). Fully half of Catavento is dedicated to hands-on learning, much like the Exploratorium in San Francisco (though that museum could eat Catavento for a snack). It is a place where you long to have a 10 year with whom to play with physics problems, light reflections, noises. My kids are a little young at 6 years to fully appreciate the explanations behind the fun--mostly they are interested in making noise and pulling levers.
The museum is housed in the old Palacio das Industrias, which dates from 1920. It's a crazy building in itself with animal gargoyles hanging off of every parapet. Definitely worth a visit. Afterwards you can head to the giant Municipal Market for lunch!