I always find the Field Museum enjoyable because there are so many things to look at. You're bound to learn something new each time you go. It's a great place to bring kids if they're the curious type.
As a child, I remember being excited to see the Egyptian exhibit because they have a reproduction of a pyramid and you can imagine what it is like to go to a real one. As an adult, it's not as impressive.
The rock and mineral collection is beautiful, and worth looking at if you like earth sciences. They do have 'Sue', the famous most complete Tyrannosaurus Rex, and they have changing exhibits throughout the year.
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