A 9-hour layover is the "sweet spot" that allows you to leave the airport and explore the local city without significant stress. After clearing customs, you typically have about 4 to 5 hours of "true" exploration time once travel to the city center and security return are factored in. If your layover is in a city with excellent rail links (like Amsterdam, Zurich, or London), you can easily visit a major museum or enjoy a traditional sit-down lunch. If you prefer to stay at the airport, look for airport lounges that offer day passes; these provide showers, hot food, and quiet areas to nap, which are invaluable for long-haul travel. Many major hubs also feature transit hotels that rent rooms in 4-to-6-hour blocks if you desperately need horizontal sleep. If you are at a hub like Singapore Changi or Seoul Incheon, you can even take a free, organized city tour offered by the airport specifically for transit passengers, ensuring you get back to your gate in time for your connection.