If São Francisco is the elegant church, Pilar is the opulent one. The dimly lit interior is one of the most heavily gilded in the Americas: walls, altars, columns, and ceiling all covered in gold leaf, with carved cherubs and saints emerging from every surface.
The church houses a small Museum of Sacred Art in the basement, with reliquaries, processional silver, and one of Brazil's most important collections of colonial religious objects. Don't skip it — the museum is included in the ticket and adds half an hour of genuinely interesting material.