When as children we first draw a house, the most common shape is a triangle on top of a box, with a door, window and chimney, and a few trees around it. And perhaps, to complete the picture, a happy family. A house surrounded by nature is a universal archetype of tranquillity and happiness. And Alentejo, a region in southern Portugal, may well be an ideal location for such archetypical happiness.

The traditional boxy house with a pitched roof is one architectural shape that everyone can design and build with confidence. Alentejo buildings, as revealed in a Portuguese survey of traditional architecture, follow this predisposition for a simple, recognizable shape, and the undulating landscape of the region is dotted with specimens of this architectural type.

A farming region that is under pressure from global primary producers, Alentejo is urgently engaged in switching from an agrarian economy to eco-tourism and leisure. With this in mind, the municipality of Mora, in the northern part of Alentejo, is investing in infrastructure aimed at consolidating this new direction in an economically, socially and environmentally sustainable manner.

One such venture is located in the Gameiro Ecological Park, an area with a river beach, a nautical club, picnic areas and a camp site. The landscape, with its mix of cork and olive trees, is typical of this region. In 2004, the municipality launched a design-and-build competition for an aquarium to showcase the biodiversity of the Iberian river, from the head waters to the mouth. Lisbon-based Promontório architects were the winners.

The site is a natural basin formed by the confluence of two small rivers, an ideal location for an explor­ation of the theme of running water. The climate here is hot – very hot. It has one of the highest numbers of sunny days per year in Europe and traditional architecture recognized that cooling and shading is the key to comfortable living conditions. The aquarium project addresses this fact in a striking way: a compact white volume with a single pitched roof made up of a sequence of precast concrete trusses spanning 33 metres between supports. The profile? Indeed, it is an oversized interpretation of the traditional whitewashed architecture known locally as „Montes Alentejanos“. The sequence of concrete ribs is the perfect strategy for sun protection and cross ventilation of the interior which is made up of a series of closed boxes containing the aquarium programme. In order to regulate the interior environment – light, humidity, temperature – and to protect the aquatic specimens, the boxes have windows on only one side.

Reception, ticket counter, shop, cafeteria, temporary exhibition space, documentation centre, research and education, live exhibits, multimedia and a small auditorium – are all lined up beneath the protective roof. The aquarium is like any exhibition space of this kind: dark for the sake of the exhibits, clearly laid out in order to educate. At the rear, a bridge takes the exhibition route outside to where a lake acts as a natural display case for local flora and fauna. A winding path takes visitors back inside the aquarium.

There was no need for big gestures here, so Promontório delivered a project that is compact, simple and clear while still managing to accommodate a complex programme. From a distance, it seems like just another big house in the countryside.