For anyone interested in technical stuff, do not miss the Technisches Museum (Tech Museum) in Vienna. It features giant old trains and a great variety of experimental scientific displays. It’s a great learning venue for kids as well as grown-ups with even a special kid’s area. I have two small kids (2 yrs, 5 yrs) and they love it! Great for rainy days! For more info – http://www.technischesmuseum.at/.