buried treasure
1. Literally, treasure (such as gold, jewels, or other valuable items) that has been buried under sand or lays hidden in the ocean. Every kid dreams of finding buried treasure at the beach.
2. Anything that has lain dormant or undiscovered for a long period of time that, upon discovery, is found to be of great value. The writer, who was unknown in his lifetime, became hugely popular after the buried treasure of his unpublished manuscript was discovered among his belongings.