La Cité de la Mer (city of the sea) is Cherbourg's maritime museum. It's huge and definitely a "must see" sight. The highlight of the museum is a decommissioned nuclear submarine from the French Navy that you can walk through with an audio tour. We'd heard of the umbrellas of Cherbourg but had no idea that they built — and still build — submarines here. In addition to the submarine, there's a small aquarium with some fish we'd never seen before and an interactive deep sea mini-sub simulation that was quite cheesy. It was all fun, though, and we spent most of an afternoon here.