In 2002, architect Adam Reed Tucker filled eleven shopping carts with Toys R Us Lego sets, hauled them home, and started building. In the decade and a half since, Tucker’s work has become a second career. “Brick by Brick,” which opened earlier this year at the Museum of Science and Industry, includes Tucker’s renderings of 13 of the world’s great architectural feats. He designs them all in his mind—no computer models and minimal sketching.

Tucker sees his work as taking architecture's intimidation factor down a notch. The bricks don't require skill, he says, because they come with built-in instructions: You can only put two bricks together in so many ways. Ask two people to make a Lego square, and, "your square is going to look like my square," he says. But Tucker isn't building squares. Across the exhibit, he spent an average of 89 hours designing and 105 hours building each structure. Add it all up, and that's 63 40-hour work weeks. The man isn't playing: “I would challenge anyone to look at my structures and see them as toys.”

Here are some of Tucker's most unbelievable works—and how he made them.