My friend and I went on here on impulse to skip out on airshow traffic. It's since become a post-airshow tradition to walk off our sunburns in the Cod.
The staff are enthusiastic and passionate about the preservation of the ship. They know the boat inside and out, and will gladly talk to you about anything. If they don't know, they'll help you look it up. It's top-notch historical interpretation.
Walk through the sub slowly. Take your time and appreciate the size of the place in relation to your own body. Think about being 18, away from home for one of the first times in your life, and living in this metal tube in a place so foreign it might as well have been another planet. Think about your own experiences, and use it to get some perspective on your life. Admire the engineering that went into the boat, all done without computers. This is solid, pen-and-paper engineering here.
Also, this is one of the most complete WWII submarines in existence, and WE HAVE IT IN CLEVELAND! Why more people don't tour this is beyond me, especially since it's cheaper than going to a movie.