Dr. Seuss, who died in 1991 at age 87, still continues to surprise. Dr. Seuss’s Horse Museum, a new book based on an unfinished manuscript and sketches he created, presumably in the early 1950s, will be published by Random House on September 3 with a 250,000-copy first printing. In this celebration of the many ways we view and appreciate art, a genial horse guides kids through a museum filled with works spotlighting horses, created by a panoply of renowned artists that includes Rosa Bonheur, Deborah Butterfield, Alexander Calder, Pablo Picasso, and Jackson Pollock.

In 2012, 21 years after her husband’s death, the late Audrey Geisel was cleaning out his La Jolla studio when she found a box containing the material that would become Horse Museum. (The box also held the author’s manuscript and sketches for What Pet Should I Get?, which Random House published in 2015.)

Under the direction of Cathy Goldsmith, Geisel’s longtime art director and currently president and publisher of Beginner Books, Andrew Joyner completed the illustrations for Horse Museum in Seussian style, integrating photographic reproductions of the artwork and slipping images of familiar Seuss characters into the museum scenarios. Goldsmith is the only remaining Random House executive who worked directly with Geisel. She shared some thoughts about shepherding Dr. Seuss’s Horse Museum into print.

What was your initial reaction to seeing the manuscript and sketches for Horse Museum?

I was very intrigued when I first saw them. This was a different kind of Dr. Seuss project. It is nonfiction and it’s not in rhyme. And how interesting that Ted chose to discuss the creative process with horses, not cats or dogs or cows, as the main focus.

How did you come to line up Andrew Joyner to complete the sketches for the book?

While we were discussing selecting an illustrator, we saw materials for The Pink Hat, which Andrew was writing and illustrating for our Schwartz & Wade imprint. He had already begun creating new art for an out-of-print Beginner Book called The Hair Book, and the two projects made it clear that Andrew was the illustrator we needed. He is talented and easy to work with—a thinking illustrator who did amazing samples showing how he would combine illustration with photographic reproductions of pieces in the museum’s collection. Andrew was inspired by Ted’s work without being limited by it. I think Ted would have loved Andrew’s illustrations for Horse Museum.

Did your work on this book evoke memories of collaborating side-by-side with Ted?

Working on Horse Museum brought back happy memories of the projects I worked on with Ted when he was alive. The challenge was to bring the book to life in a way that would resonate with today’s readers while being true to Ted’s vision of the project.

What do you think readers of this book—kids and adults—will learn about Dr. Seuss that they didn’t know before?

Readers will see another aspect of Dr. Seuss. With books like The Cat in the Hat and Green Eggs and Ham, Ted wanted to show that learning to read could be fun and easy. Here, Dr. Seuss introduces us to art appreciation and the creative process, both of which were important concerns throughout his life. I am excited by the thought that Horse Museum may well be some readers’ first glimpse into a museum.

And do you hold out hope that there are other yet-to-be discovered Dr. Seuss manuscripts and sketches hidden away somewhere?

Absolutely! That would be incredible.

Dr. Seuss’s Horse Museum by Dr. Seuss, illus. by Andrew Joyner. Random House, $18.99 Sept. ISBN 978-0-399-55912-9