If you tend to get seasick, cabin location is really important. It is a question of engineering, really. The lower and more central you are in a ship, the less roll and sway you will feel. Even if you choose a balconied stateroom, choose the lowest level and the most midship one you can find. The higher decks and cabins at the very front (forward) or back (aft) of the ship will rock and roll the most.
In this age of mega-ships, cabins now come in all shapes and sizes. In addition to the typical boxy inside and outside cabins, you can find expansive suites, duplexes and lofts. Balconies also range in size from small affairs barely able to squeeze in two chairs and a drinks table to huge wraparound decks with outdoor dining tables and hot tubs.
Some cruise travelers prefer their cabins to be near to (or far away from) specific areas of the ship. Sun-worshippers might prefer an upper-deck location close to the pools and sun decks, while partiers might want easy access to midship entertainment hubs. Travelers with mobility concerns may prefer a stateroom close to a bank of elevators.
Exception: Carnival has several cabins which are classified as inside cabins but actually have a french glass door which allows light into the room (no balcony, but the door can be opened). Carnival also has some cabins that have a window, but because the window has an obstructed view (that means there is a railing or object in the way) it is listed as an inside cabin. Royal Caribbean has some cabins that have a window but look out over an inside promenade area. These are called "promenade staterooms".
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