Arosa offers an extraordinary geographic configuration of natural bowl surrounded by mountains. A place where the comparison between man and nature is a constant emphasized by the powerful landscape and where the ancestral fight between man and mountain is evident. The site for the new structure Berg Oase is characterized, next to the great hotel, as free space and park at the foot of the rear mountain. We imagined to build without building, to assert the presence of the new through the emergent parts (artificial trees as metaphor of nature) and to leave interred the great volume with the functional program. The cover of the hypogeal spaces becomes a stage marked by geometric vegetal presences that rouse the visitor curiosity. This particular context therefore suggested us an intriguing solution, of visual impact and, above all, of great respect for the surrounding village. The great volume disappears into the earth; only the vegetal and, at the same time, mechanical “antennas” emerge, marking the recreational and collective character of the structure.The inner space appears as a terraced continuum with the slope to limit the excavation works. Further to the client’s indications, the modular design of the plant allows the maximum flexibility in the organization of the different functions. The different areas of Berg Oase are characterized by their interrelation and by their privileged relationship with the environment through technological trees that guarantee natural light and an extraordinary sight towards the landscape as well as becoming signals of the internal life at night through the artificial lighting that gives to the whole resort a magic atmosphere. The external spaces (sauna, solarium, swimming pool) are reachable directly from the swimming pools and set on a attractive terracing, dipped into nature. The new structure is accessible through a glass walkway from the existing hotel as well as (for the external visitors) from the entrance level to the hotel. The new building, beyond the “unbuilt space“ of the ”leaves“, resolves the relationship with the existing hotel and the ground through a great wall in natural stone. The external public space is therefore redesigned in order to create a cosy atmosphere and to solve the car parks problem thus discreetly integrated in the plan.