Diggers, meaning "diggers," are people who are interested in exploring man-made underground structures. Modern digging is a youth subculture and needs its own mythology, legends and even some kind of quasi-religion. The leader of Russian diggers Vadim Mikhailov, the founder and leader of the international and Russian "Diggers" movement, is considered to be the founder of the "Inner World" Digger philosophy. The philosophy of "Inner World", according to Vadim Mikhailov, is the "foundation and concentrator of life of a modern man" in the conditions of underground space and underground time. The basis for this philosophy is the idea of our planet as the Hollow Earth.Diggers are convinced that the Hollow Earth theory, together with the philosophy of the "Inner World", is a science, a myth, an emerging religious cult, and esoteric knowledge.