Yes, you can stay at Adolfo Suárez Madrid–Barajas Airport (MAD) overnight, as the terminals remain open 24/7. However, your experience will vary significantly depending on which terminal you are in. Terminals 4 and 4S are the most modern and offer more comfortable seating options, including some "armrest-free" benches that are highly coveted by travelers looking to lie down. If you have already cleared security and are in the transit area, the environment is much quieter and safer than the public "landside" arrivals halls. For those seeking actual sleep, the "Air Rooms" in Terminal 4 offer private rooms by the hour or for the full night. If you choose to stay in the public areas, be prepared for regular security patrols and cleaning crews; keep your belongings secure and your boarding pass handy, as staff may check it to ensure you are a ticketed passenger waiting for a flight the following morning.