On the grandest stretch of Barcelona's Passeig de Gràcia — a boulevard so thick with Modernista jewels that locals call it the Block of Discord — one building stops every passerby cold. Casa Batlló shimmers like a living creature: scales of iridescent ceramic, a roofline that breathes, skulls carved into stone balconies. It was commissioned by a wealthy textile magnate, transformed by a visionary architect, and completed in 1906 as a statement that would redefine what a city building could be. This is its story.