Start by naming any country that France borders. Then name any country that borders any of those countries. Then keep going until there are no more countries left to name.
The first half a dozen I entered didn't go in - how can Palmer's Green, Hanwell, Harrow-on-the-Hill not be an overground station? You must have left out half the overground lines.
Palmers Green is Great Northern
Hanwell is Elizabeth Line
Harrow-on-the-Hill is Metropolitan and Chiltern
Overground is a separate brand for the following routes:
Euston to Watford Junction (via Willesden Junction)
Liverpool Street to Chingford, Enfield Town and Cheshunt (via Walthamstow Central or Seven Sisters)
Gospel Oak to Barking Riverside
Romford to Upminster
Stratford to Richmond and Clapham Junction (via Willesden Junction)
Highbury & Islington to New Cross, Crystal Palace, West Croydon, Clapham Junction and Battersea Park (via Canada Water)