We came up Thursday on the Caledonian Sleeper, an overnight train from London that starts off as one lengthy train and then splits into Highland and Lowland sections overnight. I am very fond of trains; when I was ~8 we had a family holiday in Europe with a lot of trips via couchette sleepers, and I found them absolutely fascinating (bunks on a train! Odd thick paper sheets! train design instantly familiar when I saw it again in a volume of From Eroica with Love, of all things) and so I really wanted to give my kids their own no doubt equally odd associations.
( Lengthy digressions. )