Also known as San Pedro el Viejo, and roughly the same size as San Nicolás, this is Madrid's second-oldest church and boasts the city's other remaining Mudéjar tower, said to still be in its exact original form. Built in the 14th century, the tower has a slight incline and has been jokingly called Madrid's answer to the Leaning Tower of Pisa. (For a more modern comparison with the famed Italian structure, see the listing for KIO Towers.)