Although this is a one-of-the-kind hotel, there are now two... One in Austria - Ottensheim and the other near Essen in Germany. They have been designed from the outset to use worldwide standard concrete drainage or sewage pipe sections - so you could well see more of them in the future.
The idea of Andreas Strauss in 2004, the first rooms were provided in Linz. Moved to nearby Ottensheim, rooms are accessed by a digital keypad, whose code is provided by the self service website upon booking acceptance.