EXCLUSIVE: 'Outlander' Behind-the-Scenes Secrets of New Season 3 Sets -- Claire's Boston Home & Jamie's Cave!

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Outlander's third season will feature some truly stunning and highly anticipated new sets – and only ET has your exclusive behind-the-scenes secrets!

We teamed up with Starz and traveled to Outlander's production stages in Glasgow, Scotland, to sit down with head production designer Jon Gary Steele for the inside scoop on Claire, Frank and Brianna's Boston home and Jamie's Dun Bonnet cave.

So, how far in advance does Steele need to design and create the period drama's new sets? "In the middle of one season, we'll start to create sketches and we'll make a model for the following season," he said.

Then, together with his "very, very talented" crew of 120 people, Steele usually has roughly four months to "get all the major, big sets done for the beginning of filming."

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One of the most ambitious sets in season three is Claire and Frank's brand new (and very blue!) Boston home. "We were basically trying to show Claire in a whole new world," Steele explained. "Trying to make it look different in many different ways via color and the furnishings, of course."

Our favorite aspect of Claire's new home, aside from the many knick-knacks, is the many shades and hues of blue and green sprinkled throughout the set. Steele confessed that their inspiration for this color palette came from a very unexpected place.

"We were looking at car color samples -- that's how it started. We found on Ebay these different samples of car colors from the '50s and the '60s and what kept popping out to me was the different shades of blues and greens," Steele revealed. "I was talking to Gina [Cromwell] the [set] decorator and I said, 'What if we try that no matter where we are in that set, you look through and you see different shades of blue and green?' and that's kind of what we ended up doing."

Moving from a cozy home to a rugged cave, Steele admitted that there were many challenges that came along with designing and executing Jamie's Dun Bonnet hideaway.

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"We actually ended up building it all on stage," Steele said. "The exterior is out on location, but we built part of the exterior because every cave that we would go into was too hard to get a crew of almost 200 people to it. So we ended up having a place that worked to get the crew there and then we built an entrance to a cave-like space."

As for the set we know you're all dying to see -- A. Malcolm's print shop -- we're saving those details for a little later. However, Steele did confess that of all the season three sets, the print shop is his "favorite set of the year." (Don't panic, Sassenachs! We promise those print shop secrets will be worth the wait, but here's some scoop from the cast to tide you over!)

The production designer also spilled that fans should always keep their eyes peeled for special easter eggs on the Outlander sets. "The first year we hid some things in Geillis' room that were a nod to the future and people can look for that."

"We were talking about putting something in the print shop, but that's all I can say," Steele added coyly.

Outlander's third season premieres Sunday, Sept. 10 at 8 p.m. ET/PT on Starz.