We took an 8 day cruise over March Break. Here is what I learned that is relevant to exercise/fitness.
Independence of the Seas - one of the Royal Caribbean monstrously huge ships.
The boat we were on had a pretty good gym, complete with treadmills, Concept 2 rowers, bikes... lots of classes too if that's your thing. Free weights, machines. All the basics. The treadmills were especially cool - they faced forward out the front of the ship. I used one while we pulled out of the San Juan harbour, through the straight next to the old fortress... it was just amazing.
Not so cool - the running track. They put beach chairs on either side, just inches from the track... leaving nowhere for beach chair users to walk except, you guessed it - the track! They would wander across, walk the wrong way, 2 or 3 abreast, completely unaware that runners were there... I didn't even bother trying, one look at it and I knew I'd be too frustrated. Stuck with treadmill.
The pools were useless for swimming, they were packed and small. At best you could bob - no way a person could exercise in them. They had a designated lap swimming time (6am-9am) but that didn't make the pool any bigger!
Holy smokes. You hear about the food on cruise ships, but it really is unreal. Buffets for breakfast and lunch, sit-down fancy dinner where you can order as much as you want (double entrées, even!). And if that's not enough, there's other food places you can pop into any time you feel like it... grab a slice of pizza or a hotdog.
I ate like a crazy person. I couldn't stop myself. I didn't try to stop myself. It was delightfully gluttonous.
Plus 5-6 pounds. I hope some of it is water weight or something, but the mirror tells me it's real. Ouch.