Five Nights on the Sleeper

A sleeper berth is a hotel room that moves, and that is the whole financial argument. The fare looks like twice the airline's headline price until you add the night you no longer need to book and the airport transfer you no longer need to take.

The costed comparison

Line item	Fly	Sleeper
Fare	£52	£139
Bag	£28	included
Airport transfers, both ends	£46	£6 tram
Hotel night	£95	included
Airport meal	£14	£9 dining car
Total	£235	£154

That is one route in shoulder season, booked eleven weeks out. On a short hop with hand luggage only and a city-centre airport, the flight wins outright. The sleeper's advantage is structural rather than universal: it converts a travel night into a sleep night.

06:40, somewhere past the pass: the window is the reason people keep doing this, and it does not show up in a fare comparison.

Berth choice matters more than the operator

Couchette, six berth — cheapest, and you will sleep between three and five hours. Fine for one night, not for three.
Couchette, four berth — the value pick. The upper bunk is quieter and has the luggage rack.
Two-berth sleeper — roughly double, with a basin and a door that locks. This is the one that replaces a hotel honestly.
Seats — a false economy over 600 km. We tried it twice and lost the following day both times.

Book the carriage end away from the vestibule door. The door, not the wheels, is what wakes you.

Practical notes from five nights

Take a 500 ml bottle you can refill, earplugs rather than headphones, and one warm layer regardless of season — heating on older stock is either absent or ferocious with nothing between. Border checks happen between 01:00 and 04:00 on some routes and the guard will want the passport in your hand, not in the bag under the bunk. Breakfast is usually included and rarely sufficient.