From Rail Yards to the Vertical Forest

Piazza Gae Aulenti

A raised circular piazza at the heart of Porta Nuova, ringed by César Pelli's glass towers and centered on a shallow reflecting pool that cascades two stories down.

You are standing on a disc of pale stone, raised a full story above the street. Below you, the old Varesine rail yards sat empty for forty years, a hole in the city where traveling circuses pitched their tents and, for a long time, an amusement park drew Milanese families. None of that is visible now. Around you rise the three UniCredit towers, the tallest in Italy when they topped out in 2012.

Their architect, César Pelli, arranged them so the highest, 231 meters with its spiral spire, catches the morning light first. Look at the pool. It is only a few centimeters deep, but it is not merely decorative. It cascades over the edge of the podium and falls two floors down, feeding a ring of light wells that brighten the shopping concourse below.

On a still day the water becomes a mirror, and the towers double. The piazza is named for Gae Aulenti, the Italian architect who turned a Paris train station into the Musée d'Orsay. Fitting, because this whole district is a station turned into something else. When you are ready, walk northeast along the right-hand edge of the square toward the two green towers you can already see.

Bosco Verticale

Two residential towers by Stefano Boeri carry 800 trees and over 20,000 plants across their staggered balconies, a vertical forest completed in 2014.

You are looking at the most photographed apartment building of the last decade. Two towers, 111 and 78 meters tall, wrapped in foliage. Not vines or creepers, proper trees. Holm oaks, flowering pears, wild apples, pomegranates.

Over 800 of them, plus 5,000 shrubs and 15,000 perennials, all rooted in concrete planters cantilevered from each balcony. Stefano Boeri and his team spent three years growing these trees in a nursery before the towers were finished. They needed to train the roots to tolerate wind at height and to accept a very specific soil mix, volcanic lapilli, peat, and bark. Each balcony is a microclimate.

The leaves filter particulate matter from the air, absorb CO₂, and cut the building's cooling load by about 30 percent in summer. Birds nest here. Butterflies breed. The towers opened in 2014, the last piece of the Porta Nuova puzzle.

They sit exactly where the rail tracks once curved around the Isola district, sealing it off from the rest of Milan. For a century, this was a wall of steel and gravel. Now it is a wall of leaves. Cross the road and walk around to the park side of the towers for the best view, then continue east into the Biblioteca degli Alberi.

Biblioteca degli Alberi

A 90,000-square-meter botanical park by Petra Blaisse, planted on former rail land with labeled tree species arranged as a living library.

This park is called the Library of Trees, and the name is literal. Over 500 trees grow here, arranged in 22 circular groves, each one a different species. Every tree is labeled with its Latin and common name, its country of origin, and the year it was planted. You can walk from the Caucasian wingnut to the Japanese pagoda tree in twenty paces.

The Dutch firm Inside Outside, led by Petra Blaisse, won the competition to design this space in 2003, but construction did not begin until 2015. The park opened in 2018. Under your feet, about a meter down, the soil is an engineered mix sitting on a waterproof membrane that seals off the contaminated ground of the old rail yards. Before planting, the earth had to be capped, drained, and rebuilt.

Look west. The UniCredit spire rises above the treeline. Look east and north and you see the old Isola, brick apartment blocks, red rooftops, the campanile of the church of Santa Maria alla Fontana. The park was designed to stitch these two worlds together.

Paths radiate from circular clearings, some paved for cyclists, some gravel for walkers, some left as grass. In summer, families spread blankets here. Office workers from the towers eat lunch on the benches. When you are ready, walk north toward the red brick buildings and find Via Borsieri.