For more than 50 years, an eccentric former monk has been piecing together a grand cathedral brick by brick, completely alone and by hand. On an avenue in the Spanish town of Mejorada del Campo, a suburb 13 miles east of Madrid, a massive, unfinished structure is the life’s work of Justo Gallego Martinez, known as Don Justo. He began the project in 1963 without construction permits, blueprints, or money—just faith. The “principal source of enlightenment has been, before anything, Christ’s evangelism,” he recently explained.

Today, the cathedral’s builder is 88 years old, and the towering Nuestra Señora del Pilar has spread to 91,500 square feet. Martinez builds according to a vision kept only in his head, using a mix of donated and recycled materials in a style that draws from such incongruous inspirations as St. Peter’s Basilica and the U.S. White House.

A thin, white-haired man with a red woolen skullcap, he rises before 4 a.m. to gather discarded materials like bricks and tiles from nearby factories and junkyards. At 6 a.m., he brings them to the site to begin his 10-hour workday. Martinez’s only downtime is a short break for a small lunch because, as he says, “if you eat too much, you do not work much.” In the cold of winter, he keeps his work limited to the structure’s innards; otherwise, his advanced age doesn’t stop him from doing much, including scaling the massive complex’s jerry-rigged scaffolding.