One Day on Earth, a Hundred Years of Immortal Cultivation

One day, a young man from the modern world went on a trip and accidentally stumbled into a mountain cave, entering another world. After becoming a mighty cultivator, he traveled through time and returned to his original world, only to discover that time flowed very differently in the two worlds: one day on Earth equaled one hundred years in the other. When the mighty cultivators of the Xuan Yuan Realm discovered this, they launched an investigation and eventually found a way to connect the two worlds. Fang Chen returned to the other realm to uncover the truth.