. . . . "Under jordens overflade"@da . . . . . . . . . . . . "Explores the different types of caves, describing how they are made and explored, the history of humans' involvement with caves, and the wildlife that live within them." . "Beneath the surface" . "Juvenile works" . . "Juvenile works"@en . . "Beneath the surface"@en . . . . . "An introduction to the network of caves that lies hidden within the Earth and how resources such as oil and coal are found and extracted." . . . "Caves." . .