Walking along Madrid's historic Calle de Toledo, you might easily pass by the Real Colegiata de San Isidro without realizing you're looking at what was once the city's cathedral. This baroque church served as Madrid's provisional cathedral for decades until the Almudena was finally completed in 1993.

The building has quite a story. It was constructed in the 17th century on the site of an earlier parish church, thanks to the will of Maria of Austria, who left her fortune to the Jesuits for this purpose. Pedro Sánchez designed it in 1620, though he died before seeing it finished. Francisco Bautista took over the project, and the church was consecrated in 1651.

What makes this place special isn't just its architecture, though the baroque facade is certainly impressive. Inside, you'll find the relics of Saint Isidore, Madrid's patron saint, along with those of his wife, Santa María de la Cabeza. The interior feels surprisingly spacious and solemn, with that particular quality baroque churches have of making you look up.

I found the history fascinating. This was essentially Madrid's main church for centuries, serving as cathedral when the city needed one. The building went through various renovations, including work by Ventura Rodríguez in the 18th century, but it has maintained its essential character.

The location puts you right in the heart of old Madrid. You're steps away from Plaza Mayor and surrounded by the kind of narrow streets that make you feel like you're walking through different centuries. The church sits at number 37 on Toledo street, and while the area gets busy with tourists, the church itself often feels peaceful inside.

Discover all the secrets of the Real Colegiata de San Isidro with our complete Madrid audio guide to understand the layers of history packed into this relatively compact space. The building represents that particular Spanish approach to baroque architecture – dramatic but not overly ornate, powerful without being overwhelming.

It's one of those places where Madrid's religious and political history intersect. For anyone interested in how cities evolve, seeing a former cathedral that's now simply one of many beautiful churches in the city center tells you something about Madrid's growth over the centuries.