The Cathedral Basilica of Saint Antoninus (Spanish: Catedral-Basílica de San Antolín) is a Roman Catholic church located in Palencia, Spain.

Just by way of comparison, the internal length of the Cathedral of Reims, reaches 138m, in turn, the height of the central nave, reaches 33m in Notre Dame de Paris; Reims 38m, 42m in Notre-Dame d'Amiens and 48m in Saint-Pierre de Beauvais, the highest of all Gothic cathedrals.

Its solid, simple and austere exterior does not reflect the grandeur of its interior, with more than twenty chapels of great artistic and historical interest.

Recent studies and excavations show that it was a military tower, and after serving this function, pinnacles and cattail were added as the sole decoration.

It is a large Gothic building, popularly dubbed as "the unknown beauty" because it is not as well known as other Spanish cathedrals, though it is a valuable building which has in its interior works of art of great value, including El Greco's painting The Martyrdom of Saint Sebastian (1576–1579) and a retablo of twelve panels by Juan de Flandes, court painter to Queen Isabella I of Castile.