In Kelly Barnhill's "The Girl Who Drank the Moon", the Land of Shadows is a parallel universe that coexists with the human world, inhabited by magical creatures and ruled by the Moon Witch.

In C.S. Lewis's "The Chronicles of Narnia", Lucy Pevensie is the first to discover the magical wardrobe that serves as a portal to the parallel world of Narnia.

In Philip Pullman's "His Dark Materials" trilogy, the Subtle Knife is a magical blade that can cut through the fabric of reality, allowing characters to travel between parallel universes.

Matt Haig's "The Midnight Library" tells the story of Nora Seed, who finds herself in a library where she can explore alternate versions of her life by choosing different paths.

In Beth Revis's "Across the Universe", the Mirror Universe is a parallel universe that exists on the other side of a black hole, where everything is reversed compared to the original universe.

In Patrick Ness's "The Chaos Walking" trilogy, Todd Hewitt is a young man who can hear the thoughts of others in a parallel universe due to a condition called the Noise.

In Heidi Heilig's "The Girl from Everywhere", the Everywhere is a parallel universe that exists alongside the human world, accessible through portals, where different historical periods and cultures coexist.

Mary Pope Osborne's "Dinosaurs Before Dark" is a children's novel where the protagonist, Jack, discovers a parallel universe where dinosaurs still exist, accessible through a magic tree house.

In Hannu Rajaniemi's "The Quantum Thief", the Quantum Realm is a parallel universe that exists alongside the human world, accessible through quantum portals, where quantum mechanics and consciousness play a significant role.

In Dot Hutchison's "The Butterfly Garden", Maya is a young woman who discovers a parallel universe hidden within a secret garden, where she encounters a group of people with extraordinary abilities.

In Rick Yancey's "The 5th Wave", the Otherworld is a parallel universe that exists alongside the human world, inhabited by aliens who have invaded Earth and are trying to exterminate humanity.

Lev Grossman's "The Magicians" tells the story of Quentin Coldwater, a young man who discovers a parallel universe where magic exists and attends a magical school called Brakebills University.

In Frank Beddor's "The Looking Glass Wars", the Looking-Glass World is a parallel universe that exists on the other side of a mirror, where the characters from Lewis Carroll's "Through the Looking-Glass" come to life.

Alexandra Bracken's "The Darkest Minds" features Ruby Daly, a young woman with superpowers who discovers a parallel universe where people with superpowers are hunted and forced to live in internment camps.

Rick Yancey's "The Infinite Sea" is a sequel to "The 5th Wave", where the protagonist, Cassie Sullivan, discovers a parallel universe called the Infinite Sea, which is home to a variety of alien species.