We checked out the massive glass spheres that Amazon is building in the heart of Seattle

Amazon is growing out of control.

Unable to be constrained by its existing offices in Seattle's South Lake Union neighborhood, it's expanding operations to three new skyscrapers a few minutes' walk south in Denny Triangle.

In the shadow of those towers will live the so-called Biospheres: three giant, glass domes, slated to open up in 2018, that will fill up with greenery and endangered species. The idea is to give Amazon employees something of an oasis in the middle of the company's famously demanding corporate culture.

While taking some meetings in Seattle this week, I stopped by to gawk at the Biospheres under construction. And they're looking pretty cool, although I have to wonder if they fit into Amazon CEO Jeff Bezos' plan to bring heavy industry into outer space.

Take a look:

Disclosure: Jeff Bezos is an investor in Business Insider through hispersonal investment company Bezos Expeditions.