Inside Amazon's new 'Spheres' office building — which has a rainforest inside

• The "Spheres" building is the centerpiece of Amazon's $4 billion office expansion in Seattle.
• A rainforest built inside of the dome will house over 40,000 plants.

Amazon is set to open the new centerpiece of its $4 billion office expansion on Monday. The aptly named "Spheres" building consists of three dome structures, with a miniature rainforest planted inside. The rainforest houses 40,000 plants from 400 species that are curated from around the world, including some that are rare or endangered. At the center of the building is a 55-foot-tall tree nicknamed Rubi. When the building opens on January 29th, it will be a place where Amazon employees can hold meetings or just take a moment to relax.