Watching the Tower at Sea, I Encountered a Supernatural Incident?

Multiple worlds + weird and supernatural + supernatural powers The protagonist, Lin Tomu, was willing to become a tower keeper at sea in order to save his sister. When his three-year contract expired with only half a month left, his colleague Wang Lei died mysteriously. In the next few days, he often heard strange knocks on the door, but he and Wang Lei were the only ones guarding the tower. There was nothing on this isolated island except the tower! After suffering mental torture, he decided to pick up a shovel and check the situation outside the door...