I've talked to a lot of travelers who "did London" on a Heathrow connection. Most of them walked to a pub near Terminal 5.

The math kills you if you don't run it in advance.

Here's a realistic breakdown of a 4-hour Heathrow layover for a non-EU traveler:

• Deplaning + walking to immigration: 15–25 min

• Non-EU passport control (average queue, non-peak): 20–40 min

• Baggage claim (if checked bag): 20–30 min

• Heathrow Express to Paddington: 15 min + wait

• Time in city before you need to turn around: Whatever's left

• Paddington back to Heathrow + check-in buffer: 45–60 min minimum

Run those numbers. On a good day, you might get 60–90 minutes somewhere near Central London before you need to start heading back. On a slow immigration day, you're eating at Heathrow.

The same calculation plays out differently at every hub:

• Amsterdam Schiphol: One of the fastest exits in Europe. Tight connections become realistic.

• Frankfurt: Long terminal walks, strict re-entry windows. Budget more than you think.

• Paris CDG: Terminal transfers alone can eat 30–45 minutes.

• Madrid Barajas: Surprisingly forgiving if you're non-Schengen-to-non-Schengen.

• Rome Fiumicino: Underrated speed — often faster than travelers expect.

• Munich: Clean, efficient, but terminal distances matter.

I built the European Layover Timing Kit to run these calculations without guessing. It covers all seven major hubs with customs/transit/re-entry buffers specific to each airport, decision pages for whether the city visit is actually worth it, and printable planning worksheets.

$19 one-time. If it saves you one missed connection or one wasted airport afternoon, it's paid for itself.

Drop any layover scenario below — happy to help you work through the timing before your trip.