Most of the cost in a European trip gets decided before you’ve packed a bag - at the moment you type in your destination airport. The reflex is always the main one: FCO for Rome, CDG for Paris, BCN for Barcelona. Those airports are expensive to fly into precisely because everyone uses them. The carriers know you’ll pay.

The second city rule is simple: fly into the region’s secondary hub, not the capital or the famous one. Then use ground transport to finish the journey. The savings on the flight frequently dwarf whatever you spend getting there.

A Few Cases Where This Actually Works

Rome vs. Naples. Flights into Naples (NAP) from London, Amsterdam, or Berlin regularly run 30–50% cheaper than equivalent routes into Rome. The high-speed Frecciarossa train between Naples and Rome takes about an hour and ten minutes and costs around €20–30 booked in advance. The arithmetic is rarely close.

Barcelona vs. Girona. Ryanair built its Barcelona operation around Girona-Costa Brava Airport, 100km north of the city. Buses to Barcelona Sants run regularly and cost under €20. If you’re heading to the Costa Brava itself - Cadaqués, Begur, L’Escala - Girona is not even a compromise. It’s the correct airport.

Amsterdam vs. Eindhoven. Eindhoven Airport handles a fraction of Amsterdam Schiphol’s traffic but serves the same country. Trains run directly to Amsterdam Centraal in about 80 minutes. In peak summer, the fare difference can fund two nights in a decent hostel.

The One Catch Worth Knowing

This only works cleanly when the ground connection is reliable and priced transparently in advance. The strategy falls apart in places where the bus to the second city is irregular, expensive, or opaque about luggage fees. Always price the full door-to-door cost before assuming you’ve won.

The other trap is timing. A cheap flight that lands at 11pm in a city where the last train left at 10:30 is not a bargain - it’s a taxi fare waiting to happen. Check the last departure from the airport before you buy.

This Works in Asia Too

Kuala Lumpur has two airports: KLIA and KLIA2, the latter used almost exclusively by AirAsia. But the more useful version of the rule applies regionally - flying into Penang instead of KL for northern Malaysia, or into Clark instead of Manila for central Luzon, cuts fares noticeably and often puts you closer to where you actually wanted to be.

The flagship airport is a habit, not a necessity.