You may see Our Lady of Lujan Cathedral in the skyline before you actually find this grand religious building. Take a seat inside if it's open or just appreciate the facade from outside.
You're spoiled for sightseeing choice when spending time in Luján. Our Lady of Lujan Cathedral is a good place to begin here, but there are many other fine places to explore. Lujan Zoo, Basilica de Lujan, and Abadia de San Benito are near the principal church and and will cap off your day nicely.