Sleep in a drainage pipe.
This is the Park Hotel in Austria (cheers Scophy) on the banks of the River Danube and its rooms are something special…you actually sleep in repurposed drainage pipes!
“The external simplicity surrounds an unexpectedly comfortable interior – full headroom, double bed, storage, light, power, woolly blanket and light cotton sleeping bag. All other hotelery devices (Toilets, showers, minibar, cafe, etc) are supplied by the surrounding public space.”
To keep costs down even further, the hotel doesnt provide any sanitation, breakfast or any other usual services you would expect from a hotel…even a budget one. The visitors are expected to use the services of existing public infrastructure.