Arcana (noun)

1. Secrets or mysterious knowledge, especially that which is known by only a select few.
2. A thing that is kept secret or remains unexplained or unknown.

Origin:

Late 16th century: from latin arcana "secrets", neuter plural of arcanus "hidden".

Examples:

1. The ancient text held the arcana of the lost civilization.
2. The scientist's research uncovered the arcana of the human mind.
3. The book revealed the arcana of the occult.
4. The arcana of the universe remained a mystery to scientists.
5. The arcana of the inner workings of the government were revealed in the leaked documents.