It's Day 15 on Survivor: Island of the Idols, and things are getting bigger and better -- literally.

Only ET has an exclusive sneak peek of Wednesday's episode of the CBS reality competition, during which "Boston" Rob Mariano decides to take his and Sandra Diaz-Twine's shelter to the next level.

"We've got a lot of extra time here on Island of the Idols. Nobody's voting us off, so I'm building a shelter like you've never seen before on Survivor," Rob says in the clip. "It's basically like the mansion of all shelters."

The Survivor legend's massive shelter is actually pretty impressive -- especially since he seems to be building it himself (Sandra is an excellent spotter, however!).

"I haven't decided yet, but I may corner off one side of the shelter just for Sandra because she snores at night," Rob explains with a laugh.

Watch the full clip in the video player above.

During an interview with ET ahead of Island of the Idols' premiere, Rob said that the hardest aspect of returning to Survivor this time around was not playing the game.

"Honestly, I think the thing that was hardest for me was not competing and not being able to go to and do the challenges and play the social game and the strategic game. But at the same time, it was pretty fulfilling to be able to kind of impart a little bit of wisdom on the new up-and-coming contestants," he shared.

Sandra -- who won Survivor twice -- didn't find her role as mentor this season as challenging.

"The crazy thing is a lot of them would say, 'Oh my god, Sandra! You're my idol!' or 'When I applied for Survivor, I talked about you.' So many people gravitated towards me in that sense. And I get not everyone is a fan, but whenever I'm out there... I gave them as much information as I could give them from the three seasons that I have played, and that's what Rob did," she told ET. "You know, for me, I just talked about the aspects of my game. And a lot of times, they don't show everything on TV. So I'm explaining to them other situations that we're shown on TV that's similar to something they're going through. So, we always have plenty of content to give them."

Survivor: Island of the Idols airs Wednesdays at 8 p.m. ET/PT on CBS.

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