The phrase "hidden caverns" refers to secret or concealed caves or underground spaces that are not easily seen or known to many people. Full definition
Use Ecco's sonar to discover hidden caverns and unlock the secrets of the (metacritic.com)
The images shift from the rotating stars of the night to deep, hidden caverns below the earth, where we find those red and sepia - toned primitive images painted on rocks — images of men and women with their children. (firstthings.com)
TUKINI & SERUA WALL: This wall dive contains a series of hidden caverns waiting to be explored. (waidroka.com)