For whatever it's worth, I had assumed that the last place a compass would work would be a large cruise ship... essentially a huge steel structure immersed in salt water.

To my surprise, they worked just fine- probably a few degrees off, but not enough to notice. Having one also came in handy in two distinct ways.

I carry one in the city every day. Most often, I find myself referring to it to get oriented quickly when coming out of unfamiliar subway stations, but, in general, I find it much easier to get disoriented in the city than in the country. It's much harder to see the sky, and you often have to walk a block or two to see how street designations progress in a given direction. Maps are useless if you don't have any idea which way is which. I'd hang on to it.