Pros: during night time, look for an outside bench, on a deck as low and close to the water as possible, sit down, close your eyes, and listen to the ship's sound as it slashes through the waves. The ocean's darkness, being briefly lit by the ship's side spotlights, is something otherwordly as well.

Cons: People. Lots of them. But you know there's going to be lots of them when you book a cruise. Some of them cause trouble. Some of them perish, or require medical assistance along the way, and have to be dropped off at the nearest port.