This work presents the development of an architectural project of a headquarters of the environment agency IDEMA (Institute of Sustainable Development and Environment) in one of the Nature Conservation Units in Rio Grande do Norte. This ECOPOSTO is characterized by the low environmental impact, attendance of thermal comfort and luminous comfort through passive bioclimatic strategies and energy efficiency, and integration with the landscape. The work was motivated by the inefficiency and the impacts verified in the previous project executed in existing Units, not corresponding to the sustainability and environment identity of the Institute. The concept of the proposal is discretion, an adapted architecture to the place with the least disturbance to the environment. Therefore, the local characteristics, climatic, social and landscape aspects were observed, as the construction material and guidelines of public work as well. The proposal aims to serve as a reference to future development of architecture projects in other places so that the company, as well as other agencies of the field, increasingly incorporate the sustainability in its agenda.