For the Milan skyscrapers Bosco Verticale, "vertical forest" in Italian, it's what's on the outside that matters.
The 256-foot and 344-foot towers are covered head to toe in more than 700 trees and 90 species of plants, an achievement that was ingenious enough to land Bosco Verticale second place in this year's Emporis Skyscraper Award.
Bosco Verticale's foliage-heavy design goes way beyond eye-catching. The green architecture really is "green."
All the plant life helps reduce smog, dampen noise levels, produce oxygen, and regulate temperatures inside the two buildings.
During the winter, sunlight can easily pass through the bare plant life and help heat people's rooms. During the summer, the leaves can block harsh rays from making apartments too hot.
Inside the building, a complex irrigation system redirects the water people use back onto the porches to sustain plant life.
Designer and architect Stefano Boeri says the added greenery also serves as a way to redefine the urban space.
"It is a model of vertical densification of nature within the city," he says.
And dense it is: If all the trees were laid flat on the ground, the forest would cover an area of nearly two acres.
Pruning the trees themselves took two years, Boeri says. They had to be specially designed to fit beneath balconies of varying heights.
Boeri's towers have already inspired others to take up the same "reforestation" model.
In Australia, the world's tallest vertical forest is currently under construction. Architect Jean Nouvel and artist and botanist Patrick Blanc have teamed up to create One Central Park, located in Sydney. The structure houses more than 190 plant species native to Australia and features teeming vines that climb up the side of the building.
In Seoul, South Korea, a 70-story urban Skyfarm stacks trees and other vegetation on a structure that, itself, looks like a mammoth tree. The concept allows for efficient crop farming without the need to leave the city.
That drive to bring the rural into the urban could end up being less of a novelty and more of the standard.
In 1800, only 3% of people lived in cities. By 1950, that rate had risen to 30%, and today it sits at an even split. In developed nations, the rate is even higher - approximately 74%.
If the trend of vertical forestation holds, we had better get used to the sound of birds chirping a little closer to home.