The 19th century was a boom time for Barcelona. By 1850, the city was busting out of its medieval walls. A new town — called the Eixample (or "expansion") — was planned to follow a grid-like layout. Wide sidewalks, graceful shade trees, chic shops, and plenty of Art Nouveau frills make the carefully planned Eixample district a refreshing break from the dense Old City. Building corners were snipped off to create light and spacious eight-sided squares at every intersection.

The vision of the Eixample was to have everything equally accessible to everyone. Each district of about 20 square blocks would have its own market, hospital, schools, parks, and daycare.

While the original vision was an egalitarian one where each zone was equal, the Eixample became an architectural showcase for its wealthy residents. While adhering to height and width limitations, they built as they pleased — often in the trendy style of the day: Modernisme.

Modernisme is the Catalan version of Art Nouveau, which flourished across Europe in the late 19th century. Barcelona was the capital of Modernisme and, especially here in the Eixample, it shimmers with its characteristic colorful, leafy, flowing, and blooming shapes.

Several of Barcelona's top mansions line the boulevard Passeig de Gràcia. Because the structures look as though they are trying to outdo each other in creative twists, locals nicknamed this stretch the "Block of Discord."

Barcelona is an architectural scrapbook of the galloping gables and organic curves of the most famous Modernista architect… hometown boy Antoni Gaudí. His Casa Milà is Barcelona's quintessential building from this era.

Casa Milà is open to the public. It shows how the organic sensitivities of Modernista architecture flowed into the domestic world. This apartment would have been rented by a wealthy businessman. It shows how the affluence of the industrial age was enjoyed on a personal level — at least by the upper class. Now an apartment could be a small palace.

Gaudí's most famous work is his unfinished Church of the Holy Family, or Sagrada Família. He worked on it for over 40 years, until his death in 1926. Work continues on the church, which is not expected to be completed for another 50 years.

The Nativity Facade, the only part of the church essentially finished in Gaudí's lifetime, shows the architect's original vision. Mixing Christian symbolism, images from nature, and the organic flair of Modernisme, it's an impressive example of Gaudí's unmistakable style.

The more modern Passion facade has a different, yet complementary, style. In the soaring nave, Gaudí's columns blossom with life. Gaudí was a devout Catholic. Part of his religious vision was a love for nature. He said, "Nothing is invented; for it’s written in nature first." His little windows let light filter in like the canopy of a rain forest, creating space for an intimate connection with God.

Stepping into this monumental construction zone, visitors see the slow-and-steady progress… and what their steep admission fee is funding.

Like the construction of great churches through the ages, this project takes many lifetimes. Gaudí knew he'd never see it finished, as do the architects working on it today. Yet they all contribute, pushing steadily toward completion.

Someday a central 550-foot tower of Jesus will rise above all this. It'll dwarf everything we see today. The vision: to shine like a spiritual lighthouse visible even from out at sea. If there's one building on earth I'd like to see, it's the Sagrada Família… finished.

For a more playful dose of Gaudí's architectural genius, we're heading out to his colorful Park Güell.

While today the grand stairway and its welcoming lizard are overwhelmed by fun-seekers, Gaudí intended this 30-acre garden to be a 60-residence housing project — a kind of gated community. Fanciful viaducts compliment the natural landscape. Gaudí actually lived in this mansion. As a high-end housing development, the project flopped. But a century later, as a park, it's a huge success.

As you wander, imagine that the community succeeded, and you were one of its lucky residents. Here at the "Hall of 100 Columns" — the intended produce market — you'd enjoy the fanciful columns and decor while you did a little shopping. Heading home, you'd stroll down the playful arcade — like a surfer's perfect tube, it's another nature-inspired Gaudí fantasy. And, on such a beautiful day, you'd sit a spell on Gaudí's ergonomic benches to enjoy a grand view of this grand city.