Happy Little Submarine: Journey To The Center Of The Deep Ocean

潜艇总动员8：地心游记 (original title)

Synopsis

In order to study the mysterious substances on the seabed, he followed his uncle, the geologist "Ironstone", dived deep into the Mariana Trench, accidentally was involved in the cave maze, came to the huge unknown world and discovered ancient creatures, and started an exploration of the undersea geocenter.