Consider the following idiom:
Тут сам чёрт ногу сломит.
As I perceive it, it describes something very complex that one can hardly get through. It can be either something physical like a maze or jungles or something conceptual like a piece of music to be played, a math problem, crossword puzzle, circuit diagram of some electronic device, some complicated statistical database, etc.
I wonder if there is some other idiom in Russian describing pretty much the same thing, yet without the word "чёрт"?