Underground City XXI (UCXXI) is collaborative European cultural&art project, established by LIBAT (Fr), Labin Art Express XXI (Hr), Nomad Theatre (A), Prague College (CZ), aiming to creation of an interractive digital social sculpture. An utopia city model will be created and presented as an artistic 3D multi-user environment and society, shared and distributed on Internet, based on the heritage, dimensions and situation of the ex-coal mine in Labin/Croatia, once upon a time proprietry ex-Yugoslavia, Italy, Austria, Germany and France.