Frankfurt Airport (FRA) is a massive, sprawling hub, and a "good" layover time depends on your itinerary. For Schengen-to-Schengen connections (e.g., Paris to Berlin), a 60-minute layover is usually sufficient. However, for International-to-International or International-to-Schengen connections, you should aim for at least 90 to 120 minutes. This allows time to navigate between Terminal 1 and Terminal 2 via the SkyLine train and, more importantly, to clear the often lengthy passport control and security re-screening lines. Frankfurt is notorious for long walks; it is not uncommon to spend 20 minutes just walking from your arrival gate to the central transit area. If your layover is under 60 minutes, you risk missing your flight if your first leg is even slightly delayed. For travelers wanting to visit the city center (the "Römerberg"), a minimum layover of 6 hours is recommended, as the S-Bahn train ride takes 15–20 minutes each way, and you must account for clearing customs and re-entering security upon your return.