Cradle of the Star Sea

In 2287 AD, the sun suddenly entered an unstable period of flare eruptions, and Earth's ecology collapsed completely within three years. The Human United Government launched the "Ark Plan," sending the last one hundred thousand survivors aboard twelve generation starships toward Proxima Centauri—a journey expected to take six hundred years. But in the thirty-seventh year of the voyage, an unexpected gravitational anomaly threw the flagship "Homeward" off its established route, plunging it into a star region never before charted. There, they discovered a planet enveloped by an ancient energy shield, its surface bearing a giant ring-shaped structure stretching thousands of kilometers—the ruins of an alien civilization that had existed millions of years before human civilization, and they called it the "Cradle." — Description from novelcodex.orgFull novel: Cradle of the Star Sea — read the rest free on N​o⁠v​e⁠l​C⁠o​d⁠e​x⁠.​o⁠r​g⁠