Paris
London to Paris on EuroStar is so easy even with an early start. Paris mainline stations are large and include the integrated Metro and RER lines; the equivalent of London's tube and overground. The signage is excellent with numbered metro lines and lettered RER lines with colour coding a primary school teacher would die for. From the EuroStar terminal you can wander towards the Paris network and buy your NaviGo card (also called easy passe) loaded with a carnet of 10 tickets from a ticket office being careful to avoid the long queues of the mainline ticket offices.