A main mystery in Silo is where the big underground cities came from and why they were built. Now, after seven episodes of the third season, we still don't know why, but we are learning who built them.

Congressman Daniel Keene and journalist Helen Drew have had a strange journey in Season 3's flashback story. They looked into what happened to Daniel's sister on a mission in Iran, were followed by a mysterious man, and even had their car take them away.

Episode 7 brings some answers. After their car took them away, they met Senator Thurman, who introduced them to billionaire Per Stensen. Stensen said they would get all the answers if they signed a simple agreement.

Senator Thurman said, 'Once we've signed, you'll get on the plane, and this time tomorrow you'll know everything.'

When the plane landed in Atlanta, Georgia, Stensen told Helen the next part of the journey would be by helicopter. She asked where they were going, and he said it was one of his properties.

Stensen said, 'It's 300,000 acres, 400 square miles, and used to be 42 farms.'

In the last scene, we finally see what they are going to see.

Senator Thurman said, 'I wasn't being dramatic, this is about saving the world.'

Helen asked, 'What is that?' and the senator said Daniel, who knows engineering, would know.

Daniel said, 'It's a big drill,' looking out the window.

The drill Daniel saw is the same machine we've seen before, now sitting in a watery cavern deep in Silo 18. It's clear that this is the start of the silos being built.

The people behind the project are Senator Thurman, who believes in the vision, and billionaire Per Stensen, who is funding it and thinks it's about saving the world.

Big questions remain, like what happens to the world that forces everyone underground, and who is in charge of the silos hundreds of years later.

Silo Season 3 is now streaming on Apple TV, with new episodes every Friday.

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Silo Season 3 is on Apple TV now.

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