Virtually all modern cruise ships are equipped with multiple swimming pools, serving as a central feature of the ship's outdoor leisure and entertainment decks. The number and variety of pools often depend on the ship's size and target demographic. Large "mega-ships" from lines like Royal Caribbean or Carnival often feature four or more pools, including family-friendly main pools, adults-only "Solariums" or "Serenity" areas, and even high-tech "infinity" pools that overlook the ship's wake. Many ships also incorporate dedicated water parks with slides, "FlowRider" surf simulators, and splash pads for children. In addition to standard pools, most vessels offer several heated whirlpools or hot tubs. To accommodate different climates, some ships feature "Magrodome" retractable glass roofs that can cover the pool area during inclement weather or cold-weather itineraries (like Alaska or the Baltics). Water in the pools is either filtered seawater or chlorinated freshwater, and most pools are drained and refilled regularly for hygiene and safety.