“It was like returning to the roots of architecture,” Álvaro Siza says about the experience of creating a small chapel at the top of a hill, on former farmland in Portugal. The first project by the Portuguese Pritzker Prize–winner to be built in the Algarve, the country’s southernmost region, it would also be the first part of a larger spiritual retreat. The pristine sanctuary is pure form—devoid of plumbing, HVAC, and electrical systems.

The plan took shape two years ago, when the clients, a Swiss/American couple who met and married in Portugal in the 1980s, approached the architect. They wanted to develop a self-sustaining project in the region and asked him to design a focal point. “A chapel seemed like a good way to start,” they explained. Overlooking their property, such a building, they felt, would set a positive tone for the land’s future development.