Three years ago, Amazon's horticulturalist was giving CEO Jeff Bezos a preview of what the company's three plant-filled Spheres – the centrepiece of its US$4 billion (NZ$5.4b) downtown Seattle office project – would look like on opening day.

The glass orbs were built to let Amazon workers escape from emails, meetings, reports and deadlines to walk along stone paths beside waterfalls, let ferns from South America brush their shoulders and the moist, tropical air fill their lungs.

The trickiest part of the project was transporting a 16.7m-tall tree nicknamed Rubi (short for Ficus rubiginosa) from a southern California farm to downtown Seattle, where it was hoisted by crane last summer and dropped through a hole in the roof.

Wi-Fi is available for those looking to work, as well as small meeting spaces like the "bird's nest", perched along the suspension bridge beneath Rubi that resembles a tree fort swaying in the branches.

Besides creating a park-like setting where workers can recharge, the spheres will serve as a recruiting tool, said John Schoettler, who runs Amazon's global real estate division and oversaw the project.