In terms of preservation, including the architectural and sculptural details that typify “Guaraní baroque,” San Ignacio Miní may be the best surviving example of the 30 missions built by the Jesuits in a territory that now comprises parts of Argentina, Brazil, and Paraguay. It’s a tourist favorite for its accessibility in the midst of the present-day village of San Ignacio.

San Ignacio’s centerpiece was Italian architect Juan Brasanelli’s monumental church, 74 meters long and 24 meters wide, with red sandstone walls two meters thick and ceramic-tile floors. Overlooking the plaza, decorated by Guaraní artisans, it’s arguably the finest remaining structure of its kind; the adjacent compound included a kitchen, dining room, classrooms, and workshops. The priests’ quarters and the cemetery were also here, while more than 200 Guaraní residences—whose numbers reached 4,000 at the mission’s zenith in 1733—surrounded the plaza.

Founded in 1609 in present-day Paraguay, San Ignacio Guazú moved to the Río Yabebiry in 1632 and to its present location in 1697, but declined rapidly with the Jesuits’ expulsion in 1767. In 1817, Paraguayan troops under paranoid dictator Gaspar Rodríguez de Francia razed what remained.

Rediscovered in 1897, San Ignacio gained some notoriety after poet Leopoldo Lugones led an expedition here in 1903, but restoration had to wait until the 1940s. Parts of the ruins are still precarious, supported by sore-thumb scaffolding that obscures the complex’s essential harmony but does not affect individual features.

Visitors enter the grounds through the Centro de Interpretación Regional, a mission museum (Alberdi between Rivadavia and Bolívar, 6 a.m.–7 p.m. daily, US$1). A nightly light-and-sound show, lasting 50 minutes, costs an additional US$1. Outside the exit, on Rivadavia, eyesore souvenir stands detract from the mission’s impact.