I honestly don't know much about them. I've never been on a Disney at-sea day (other cruise lines, pre-children) and with two in a row plus another later in the week I just fear cabin fever. I don't mean we'll sit in our room the whole time, just more so full-boat cabin fever. As I said, share your experiences, tell me what you all do, please prove me wrong. We're amateurs, only one (short)
Disney cruise under our belts.
Gotcha. OK, in short, sea days are awesome. We actively look forward to them, and have never felt any sort of "cabin fever" on the Fantasy or Dream. As
@PrincessShmoo pointed out, you won't get bored for lack of things to do on the ship. And if you decide you want to do nothing at all, that's cool as well.
Don't get me wrong - I like a lot of the port days, too. However, those involve a measure of "hustle and bustle", whether you're making your own way into the port or you're part of a Port Adventure. Either way, you're on a schedule - get up at a certain time, leave the ship at a certain time, get back to the ship at a certain time - and you have to prepare in advance for things like sunscreen, bug repellent, pocket money, passports/KTTW cards, water, snacks, etc. (we have three school-age kids). I'm not saying these are "deal-breakers" for Port Adventures by any means, but sea days are a nice break from all of that.
You get up when you want. You go up to eat when you want. Catch a movie. Take a swim. Send the kids to the clubs and grab an adult beverage by the adult pool. Head to the Rainforest Room for a while. No schedule. No timetable. No loading yourself up like a pack mule before being herded like cattle off the ship. No negotiating cab fares or with straw market vendors.
Very leisurely. And bonus - the ship might not be super-crowded on the sea day since you are looking to sail at an "off" time not tied to a U.S. school vacation period.
I really don't view sea days as a negative. Quite the opposite. Unfortunately, the sea days go by a lot quicker than you'd think.