The specific differences will depend on the ship you’ll be traveling on, however, in general, main deck cabins have windows, upper deck cabins typically have larger, picture windows and/or balconies. They’re a bit brighter, but they may be a little noisier compared to the cabins below deck. The lower deck cabins have portholes, offer more privacy, and they’re quieter and a bit more spacious on certain vessels due to the vessel design.