Galileo's middle finger
One of the highlights of our trip to Italy was visiting the History of Science Museum in Firenze (Florence) where they have a couple of Galileo's telescopes.(Maybe these are the only ones in existence, actually.)
It's a fascinating museum, and makes an especially nice change if you've made your feet sore for a week looking at liturgical art in churches. Although the display with Galileo's finger did remind us uncomfortably of the many holy relics we saw at the Medici chapel and elsewhere—splinter of the "true cross," anyone? The Medicis were clearly a gullible bunch, but that's another story. They're also largely responsible for this museum.
The collection is massive—room after room of beautifully preserved instruments, sometimes dozens of versions of the same thing. It's not just astronomical objects, but all science: mechanics, optics, barometry, fluid dynamics, medicine. Instruments for measuring as well as didactic devices to demonstrate physical laws and properties.
My only complaint is that you really needed an item-by-item guide in English to appreciate what you were looking at. I've just discovered that such a thing is available on their website, but of course that didn't help at the time. Still, now I can learn more about some of my favorites: the Jovilabe, the Lady's Telescope (complete with beauty cream), the Astronomical Compendium, and Galileo's inclined plane, which one of the docents kindly demonstrated for us.