Baroque style triumphs in all its glory inside the basilica. Walk down the only nave: as you will have noticed, the pillars as well as the columns embellished by capitals with leaves called Corinthians are all arranged diagonally: this optical trick also serves to add an effect of grandeur greater than the limited amount of internal space. Among the eight chapels of the church, stop for a moment at the second one on the right, which is dominated by the magnificent image of Santísimo Cristo de la Fe y del Perdon. This is this statue that, as I said before, is carried in procession on Palm Sunday at sunset, thus ushering in the Holy Week and all the corresponding processions.
Now sit down at one of the first rows of benches and look up at the beautiful frescoes of the dome by the Italian-Swiss painter Bartolomeo Rusca. They depict the young martyrs Justo and Pastor's assumption into heaven, alongside the González Velázquez brothers. You can also admire the beautiful eighteenth century organ on the platform behind you, which is one of the most popular in all of Spain.
FUN FACT: probably at least once in your life, you've heard the famous "Minuet" by Boccherini. The great eighteenth-century Italian composer Luigi Boccherini died in Madrid and was buried in this church, until Benito Mussolini ordered for his remains to be transferred to Italy, in the city of Lucca.