For "Beyond the Horizon: A Journey through the Multiverse," a captivating book cover could feature a dynamic scene that captures the essence of the multiverse journey. Picture a vast cosmic landscape, with swirling galaxies and nebulae stretching across the background. In the foreground, have the protagonist, Alex, standing heroically, gazing out at the vast expanse of the multiverse with determination and courage.

To add depth and intrigue, include subtle hints of the different realms Alex will explore throughout the book. Perhaps a mysterious portal crackling with energy could be opening nearby, hinting at the adventures that await within. Additionally, incorporate symbols or artifacts that represent the key themes of the story, such as ancient relics, cosmic crystals, or futuristic technology.

For the title and author name, use bold, futuristic fonts that stand out against the cosmic backdrop. Add metallic accents or embossing to give the cover a tactile element that enhances its visual appeal.

Overall, aim for a visually stunning and thematically relevant cover that piques the reader's curiosity and promises an epic journey through the multiverse.