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

It's hard to miss the biospheres even when you're just walking up the street.

You don't really get a sense of how big they are until you get a little closer.

Here's all three. The closest one looks like it's got all its glass in place...

The one in the middle is only half-done, and the one closest in this picture doesn't have any glass at all.

It may seem like one big continuous piece of glass on the completed dome, but if you look closely, they're actually kind of piecing it together like a giant jigsaw puzzle.

When all is said and done, the domes will be the centerpiece of a park, complete with grass and a dog run. They're being built in the Denny Triangle neighborhood, about a 15-minute walk from Seattle's famous Space Needle.

The 100-foot tall domes, scheduled for completion in 2018, will be filled up with more than 300 plants that are endangered species, essentially turning the place into a conservation project as well.

John Schoettler, Amazon's global real estate director, recently told Bloomberg the goal was to create a "link to the natural world," so Amazon employees could brainstorm while taking a breath of fresh air in the domes.

This rendering is how Amazon envisions they'll look when it's all done.

The domes will be in the shadow of Amazon Tower I, better known as "Doppler" — a reference to the internal codename of the Amazon Echo while it was still in development. This building only opened in 2015...

...and comprises the first of three brand-new Amazon skyscrapers that will house most of the company's operations. Amazon Tower II, pictured here as of February 2016, is slated to open in September 2016, with tower III opening in 2019.

Really, all of this construction just shows how incredibly fast Amazon is growing: From 1998 to 2010, Amazon was headquartered in Seattle's Pacific Tower — a former VA hospital — but it's hiring so many people that it was bursting at the seams.

You may have noticed that there aren't really any Amazon logos on the tower or the domes. Amazon prefers to keep a lower profile — this is Day 1 North, one of Amazon's main existing buildings in Seattle, and it's totally nondescript except for the subtle name on the right here.

Similarly, this is the main plaza of the existing Amazon urban campus, about a 15-minute walk away from where the Biospheres are going up. It's very low-key, like a city college campus, and people are allowed to use it freely. It's my understanding that it even hosts farmer's markets.

I'm not going to lie, though, I was disappointed to find that they have bus shuttles to take employees back and forth between the old buildings and the new...I was hoping Amazon was shuttling them around by Prime Air drone.

In the meanwhile, here's an official Amazon recruitment video showing off its urban campus: