For an in-depth understanding of Greek mythology, Celtic mythology, Cthulhu mythology, and Norse mythology, you can refer to the following classic works of literature: 1 "Greek Mythology"(Hesiod): This is a classic Greek mythology novel written by Melville of Germany. It tells the stories of the various gods and heroes in ancient Greek mythology with vivid historical scrolls and character descriptions. 2."Celtic Mythology"(Arthur Clarke): This is a novel about British folktales. It tells about various myths and legends in England, including Celtic mythology and Scandinavian mythology. HP Lovecraft: This is a classic Cthulhu mythological novel written by the American author, Asimoff. It tells the story of the gods and monsters in the Cthulhu myth with a fictional worldview and horror plot. 4. Norse Mythology (William Gibbson): This is a novel about Norse mythology. It tells the stories of various gods and heroes in Norse mythology, including Thor, Odin, the Norse goddess, etc. These four books are all classics, covering stories and characters of different mythological systems. They are very useful reference materials for those who want to understand these myths in depth. However, it was important to note that these books were all literary works. Reading them required a certain degree of literary attainment and patience. At the same time, it also required one to choose according to one's interests, hobbies, and reading level.