Passeig de Gràcia is Barcelona's most famous street — a wide, tree-lined boulevard running through the Eixample district that happens to contain an extraordinary concentration of Modernista architecture. On a single block between Carrer d'Aragó and Carrer del Consell de Cent (known as the Manzana de la Discordia, or Block of Discord), you have three rival masterworks: Domènech i Montaner's Casa Lleó Morera, Puig i Cadafalch's Casa Amatller, and Gaudí's Casa Batlló. A few blocks up sits the even more spectacular Casa Milà (La Pedrera), also by Gaudí.
The boulevard itself is a pleasure to walk — wide pavements, elegant lampposts, and the hexagonal paving tiles designed by Gaudí. It's also Barcelona's main luxury shopping street, so the ground floors of these century-old buildings now house Chanel and Hermès. That contrast is very Barcelona.