Jules Verne's classic science fiction novel 20,000 Leagues Under the Sea was written in 1869. It asks the question, “What if a man built a vessel that could go underwater and make war upon other vessels?” He must have been inspired not only by the recent invention of a French submarine, the Plongeur, but also of the clash of the ironclads Monitor and Merrimac during the American Civil War.
A vessel that can travel underwater and attack other ships? What an insane prediction! That could never come true! And, of course, it did, although not entirely the way Verne predicted. The submarine in the novel attacks other ships with a large ram in its nose, not unlike how classical triremes would attack each other. Verne knew, or course, that a modern cannon would not work underwater, but he did not anticipate the invention of the modern torpedo.
Yet Verne's concept of the submarine also included men who would leave the sub in suits with their own oxygen supply. These suits are clumsy and heavy, requiring its user to walk slowly upon the bottom of the ocean instead of swimming, but they are harbingers of a new era of underwater exploration.
What makes this book an interesting case to teach is that it's a case where the author made predictions which have already come to pass. We as modern readers get a unique opportunity to comment on and perhaps criticize Verne's ideas. An enterprising teacher could create a series of slides from submarines from antiquity to modern submarines. (Here's a useful link for that.) One might do the same with underwater suits, from clumsy diving bells to SCUBA and beyond.
Furthermore, students could spend a lesson predicting what vessels of the future would look like and engage in the same type of thought experiment that Verne did. Any type of vessel would be appropriate: cars, ships, submarines, space craft, airplanes, etc. I would suggest in this that you hold your students to a rough sort of scientific scrutiny. Have them take ideas that exist now and predict how they will change, rather than invent ideas that couldn't exist with a violation of the laws of physics. For example, a space ship with a kind of “star drive” that would propel it to other solar systems would be okay, but a space ship that would magically teleport itself would probably not be in the spirit of this assignment.
If you're going to teach this boo, I would also recommend the fun Walt Disney movie of the book. It has some changes from the book, notably Captain Nemo is changed from an Indian to a generic European (James Mason), but it is a faithful reproduction of the spirit of the book. It's a lot a fun, especially during the battle with the giant squid.