Mt. Moon

Mt. Moon lies between and Cerulean City. It is introduced when, and  visit there in. Due to the pure darkness inside, Pokémon that can live in darkness can be found often in this place.

Part Red & Green
Mt. Moon is mentioned for the first time in when,  and  visit. Soon after, they hear an explosion in the cave. They follow the sound and eventually encounter Professor Joshua and his Pinsir. Joshua claims that he visits Mt. Moon to search for some fossils to bring back to his laboratory in Cinnabar Island, but he is attacked by two men in black uniforms. Despite of that, Redwald and his friends help Joshua find the fossils. Eventually, Redwald finds two fossils. Joshua gives Helix Fossil to Redwald as a thank-you gift and he keeps Dome Fossil. He invites Redwald to visit him in the laboratory in Cinnabar Island to bring the fossil back to life.

Geography
Mt. Moon lies close to Cerulean City. The area is so dark that the Pokémon that survive in darkness, such as Zubat and Golbat can be widely found in this area.

History
As states in, a meteorite hits this area centuries ago. The meteorite carries Pokémon from space. The Pokémon from space, which are believed to be Clefairy, Clefable, Jigglypuff and Wigglytuff adopt the life on earth. They breed with Nidorina and Nidorino as well. Eventually, they become species that is from earth-alike.