The passenger service building at the Eurotunnel Calais Terminal has a name almost nobody uses: the Charles Dickens Terminal. It is named for the British novelist who - in the years before there was any tunnel - took the cross-Channel ferry to France often enough to write A Tale of Two Cities, parts of Bleak House, and significant passages of Our Mutual Friend on what was then a much slower journey. The choice of name was a small piece of cultural diplomacy at the tunnel's opening: a French station honoring an English writer who loved France, on the day the two countries finally stopped letting twenty-one miles of water keep them apart. The British end at Cheriton, near Folkestone, mirrors the gesture: its passenger building is called the Victor Hugo Terminal, named for the French novelist who lived in Jersey and Guernsey during his long exile and crossed to the mainland often enough to make the Channel a recurring presence in his work.

The terminal has ten island platforms - long, narrow strips of concrete arranged in parallel, each separated from the next by a single track of rail. Four overbridges span the platforms at roughly equal intervals along their length. The geometry is not decorative. Cars and lorries embark and disembark from the Le Shuttle trains by driving directly off the carriages onto the platform and then up the nearest overbridge to the A16 autoroute network. The platform a vehicle uses depends on where on the train it is parked, and the overbridge it uses depends on whether it loaded near the front, middle, or rear. Bridges at the western end of the platforms handle embarking traffic; those at the eastern end handle disembarking. The track loop into the terminal runs anti-clockwise, so that the locomotive that pulled the train through the tunnel stays at the front for the return trip. The Folkestone terminal loops clockwise to balance flange wear evenly across the wheels. Every piece of the system, in other words, exists for a reason.

Under the 1991 Sangatte Protocol between France and the United Kingdom, passport control at the Eurotunnel terminals operates under what diplomats call juxtaposed controls. A traveler driving from Coquelles to Cheriton clears French exit checks and the UK entry checks before boarding the train - all on French soil, in the same building, in the same line. The UK Border Force officers in their booths at Coquelles are working on French territory under bilateral treaty; the French Border Police booths a few meters away are doing the same in reverse. The Schengen Area ends here, beneath the autoroute overbridges, four miles inland from the sea. Travelers exit France long before they leave it. The arrangement saves time, simplifies enforcement, and - critically for the British - means that anyone refused entry to the UK is refused on French soil and remains a French problem.

The trains that run between Calais and Folkestone are not normal trains. The vehicle-carrying shuttles are unusually tall and wide to accommodate the cars and lorries inside them, with a loading gauge larger than anything else on the French rail network. A standard SNCF locomotive cannot operate on the route. The shuttles cannot operate anywhere else. The entire fleet lives within the small, self-contained Channel Tunnel rail network, with major maintenance carried out at a specialized facility on the Coquelles site - one of the more unusual industrial enclaves in Europe, an island of bespoke engineering in the middle of the Pas-de-Calais marshlands. Freight shuttles started running in July 1994; passenger services began that December. Three decades on, the terminal handles millions of vehicles a year, every Le Shuttle taking thirty-five minutes to travel from one country to the other, of which only about twenty are spent underwater. The peat that had to be dug out before any of it could exist remains, somewhere, in a spoil heap nearby - the buried foundation of one of the largest engineering achievements of the twentieth century.