The Strongest Qi Refiner: 9,999th Level

This is a long novel, and the first half can be a bit of a slog. But if you have the patience to stick with it, the second half gets more and more addictive. It tells the story of a modern boy who transmigrates to a world of immortal cultivation and gets trapped on a mountain for twenty years, unable to leave. Then he gains a transmigrator's golden finger and becomes a major powerhouse.