The Sanctuary of Atotonilco, ten kilometres north of San Miguel de Allende, is one of the most remarkable interiors in Mexico. Built beginning in 1740, the inside of the church was painted over two decades by a single artist, Miguel Antonio Martínez de Pocasangre, who covered every surface — walls, ceilings, arches, vaults — with religious murals, inscriptions, and painted sculptures. The effect is overwhelming: a total environment of Baroque devotional art that has been called the "Sistine Chapel of the Americas."
Atotonilco is still a working pilgrimage site, drawing thousands of visitors for Holy Week in particular. Pilgrims walk the 12 kilometres from San Miguel barefoot, some carrying crosses or flagellating themselves — intense expressions of a religious tradition that has continued here since the 18th century. It is not a performance for tourists; this is how the community marks the calendar. The sanctuary was listed as a UNESCO World Heritage Site in 2008 alongside San Miguel's historic centre. Go early on a weekday if possible, before the tour buses arrive from San Miguel.