https://www.reddit.com/r/ChineseLanguage/comments/z21v3f/imagin8_press_has_a_lot_of_free_audio_book/ — I posted this one a long time ago but I’m putting it at the top since it’s generally the least advanced (HSK 2-4ish). The main content is a beginner’s version of 西游记 (Journey to the West). Imagin8 Press publishes graded readers which you can buy, but they also make the audiobook version of all their books available completely for free which is really generous.
[my-hsk.com](https://my-hsk.com/) has a whole bunch of audio books and stories available:
* https://my-hsk.com/category/audiobooks-for-kids-in-chinese/ — This is a collection of fairy tales like Little Red Riding Hood.
* https://my-hsk.com/category/audiobooks-in-chinese/ — Full books (some of these are probably pretty advanced).
I really, really love the version of [小王子](https://my-hsk.com/audiobooks-in-chinese/audiobook-the-little-prince-in-chinese/) (The Little Prince) there. The woman reading it does a tremendous job with the voices for different characters and setting the mood.
https://www.youtube.com/@zhongwenyousheng/playlists — This YouTube channel also has a number of books including another version of 小王子 — I don’t like it as much as the other one (and it seems to be a different version of the book as well) but it’s still quite high quality and actually has Mandarin subtitles. With the my-hsk material you’re just on your own.
https://www.youtube.com/watch?v=k0gCop58Lec — 小狗钱钱 is a (children’s) story about a white Labrador named 钱钱. He has a very special ability. The story is also probably not what you’re expecting, but the dog’s name is a pretty good hint. The man who read it is also very good, although he gets a little 夸张 sometimes.
https://www.youtube.com/watch?v=_5xt0-4uu_I — 动物农场 (Animal Farm). This is a pretty advanced one, also another very high quality performance with the reading.
https://www.ximalaya.com/sound/605795718 — A nice reading of 兔子共和国 (Watership Down). Ximalaya stuff doesn’t seem to play in the browser for me but I was able to download it with yt-dlp: https://github.com/yt-dlp/yt-dlp
https://www.ximalaya.com/album/59386928 — A performance of the Mandarin version of Blindsight (very dark sci-fi from the author Peter Watts). Unfortunately, a lot of it is only accessible to Ximalaya VIP members. By the way, Peter Watts very generously makes all his books available online for free: https://rifters.com/real/shorts.htm – those are the original English versions. Definitely my favorite author and if you like sci-fi and it can be English I’d highly recommend his work, especially Blindsight.
There you go. That should be 20-30 hours of listening material.