My vague memory from reading the novel about 4 decades ago is that artur was deliberately trapped or marooned by some competitors or criminals and I don't have mental imagery of there being multiple levels just the image of him being marooned and this beast being a hindrance to him escaping from the planet or moon he was marooned on. Btw thanks for adding these details my memory is no longer as reliable as I would like!

The only improvement I can suggest for this very pleasantly surprising answer for which (and question editing) i want to thank you (but SO frowns upon that somehow), would be: can you find a public domain audio version of the book ? PS merci