Tucked between lushly vegetated sand dunes and the Atlantic Ocean, the Mãe Luiza favela spills out from the fringes of Natal, a city of 800,000 people in northeastern Brazil. While the population of Mãe Luiza possesses a strong cultural identity because of its location at the edge of a state nature preserve, it faces challenges common to these dense outer neighborhoods—poverty, inadequate infrastructure, and a dearth of public space.

Herzog & de Meuron and the philanthropic branch of Ameropa, a Swiss fertilizer and grain dealer, partnered with a local organization in 2009 to shape A Vision for Mãe Luiza, a pro bono master plan that seeks to catalyze development in the community. The pioneering building, Areno do Morro, opened April 9.

Located on a 1.2-acre wedge-shaped patch of land a short walk from the ocean, Areno do Morro sits on the former site of an open-air gymnasium. The architect took formal cues from the original structure and, with the help of local workers, built a raw shed-like structure of steel and concrete to house an indoor athletic field used by a school and the community.

A pitched roof of corrugated aluminum panels hovers above a set of one-story cylindrical enclosures used as multipurpose spaces, a teacher's lounge, and changing rooms. The architect developed a special lightweight block with several vertical openings that allow people to see through some of the curved walls.

Inside, the arena's tiered concrete seating can accommodate up to 420 spectators to watch games of soccer, volleyball, and handball. A ramp takes visitors up to a second-floor terrace, which opens to views of the ocean.

Viewed from afar, the structure floats with the lightness of a folded sheet of paper amid a dense patchwork quilt of orange tile roofs, and, at night, the gymnasium glows like a beacon.