This 50-mile icon of American engineering has an amazing story that can be quickly told in a short documentary that I recommend. The long book by David McCullough is, I don't think, worth the read. Most people on my trip were either starting it or had finished it or were contemplating finishing it. One woman told me if she knew about the documentary she would have definitely waited to see it and was glad she didn't trudge through the second half.
While you don't really need to see the Panama Canal in person, it is a pretty cool experience going up and over a mountain on a ship, guided by little tiny trains (called mules), while a bevy of men jump on and off your boat, munching on a big basket of snacks while on board. There is a lot of rope throwing and big doors opening and water filling and emptying.
Here are some images from my recent passage through the famed palindrome inducing waterway.