Commissioned by the NGO Fundació Catalana de l'Esplai, we are working on several projects for summer camps in different areas of Catalonia, such as Castellbell i el Vilar, Navès and Sant Joan de les Abadesses, based on the criteria of sustainability, durability, adaptability and austerity that characterise the buildings we have made for them. The main premises taken into account when designing the new hostel were the following: - Economically sustainable project. The cost could not exceed 450 €/m² built, including urbanisation. - Multifunctional project. With more than 25 years of experience managing nature schools, the Foundation determines that the viability of a facility of these characteristics must have great versatility. Aspects such as the capacity of the rooms, the layout, the bathrooms, the versatility of the activity rooms and the accessibility of all the spaces. - A project that respects the environment. As an implicit part of the Foundation's educational project and with the experience acquired in a building such as the CENTRE ESPLAI, the construction of this new nature school should have energy saving systems. In the first of the projects, the proposal for implementation is based on the urban planning need not to exceed the gauge of the pre-existing buildings – ‘L’ shaped barracks in a very precarious state of health and hygiene. The new facility will consist of three distinct areas: service building, nature classrooms and dormitory area. The services building will house the dining room, kitchen, storeroom and a reception area and information point. The dining room will have capacity for almost 100 diners and will be located in a single room, where the different groups staying at the hostel will find a meeting and relationship space. In the building next to the dining room there will be three nature classrooms with a capacity for 30 people each. The proposal is for system units in which the ratio between useful and built surface area increases because the communications between them are produced from the exterior space, avoiding the conventional typologies of holiday camp houses that respond to the comb-shaped scheme -circulations from which hang batteries of bedrooms with communal bathrooms. This modular layout will permit, for example, housing different groups within the same installation and allowing them to maintain a certain degree of privacy inside their hut. The volumetric fragmentation into small autonomous units makes it possible to graduate the number of users and minimise maintenance and surveillance costs, while at the same time making it possible to configure a system with the entire colony. The unit is proposed as a reference, archetype and image of the imaginary world of childhood - small houses, village, relationship with the forest, paths and nature - and, in the future, it will allow for easy extension or expansion of the system itself. The adapted exterior routes and the passages between the different volumes allow circulation between them, grouping the entrances and facilitating control by the monitors. We propose three different types of rooms, with groups of 4, 6 or 8 children, with the possibility of developing them on one or two levels depending on the body, resulting in a total capacity of 90 places. The upper space and the volume of air it contains acquire enormous importance given the occupation of the living areas. It also favours the incorporation of acoustic control and artificial lighting on the suspended fabric formed by white tubular profiles. The simplicity of the materials used has allowed for great economy in the execution, as well as in subsequent maintenance. The interiors are made of painted fair-faced concrete block, fine-grained polished concrete floors, 20 cm wide windows inserted in 2 mm thick matt stainless steel frames with painted shutters incorporated to darken the interior and exposed chained domes that generate a warm shade of interior light. The location of the sets of windows in the vertical walls allows perfect cross ventilation, regardless of the prevailing wind in each case. For the exteriors, the unity of the material is emphasised – façades and roofs, both of living cells and public buildings, respond to the Coteterm system by Parex, a flexible, self-cleaning stucco that allows for continuity of insulation and waterproofing treatment around the perimeter. The external routes are differentiated into two types of paving: textured concrete slabs for pedestrians and scraped concrete for road traffic. Given the final solution of the proposal, the spectrum of users is widened, as it will not only be able to host summer camps and camps for schoolchildren, but also families and groups will be able to use the facility all year round.