This is the 13716th most frequent Polish word.
podmorskich
"Podmorskich" means "undersea" or "submarine" (relating to under the sea).
The word 'podmorskich' is used as an adjective describing 'głębinach', indicating 'of the undersea' or 'located under the sea'.
Odwiedzamy miejsca w głębinach podmorskich, aby badać ich ekosystemy.
We visit places in the undersea depths to study their ecosystems.
Here, 'podmorskich' is an adjective that describes 'miastach', meaning 'undersea', attributing the location of the cities to beneath the sea.
Legendy opowiadają o miastach podmorskich pełnych skarbów.
Legends tell of undersea cities full of treasures.
In this sentence, 'podmorskich' qualifies 'jaskiniach', specifying that the caves are underwater or beneath the sea level.