A seemingly plain tunnel that was
dug by wild DIGLETT.
It is famous for connecting
ROUTES 2 and 11.
As a whole, the cave runs from the northwest to the southeast, passing under Celadon City, Route 7, and Route 6 as it progresses toward Vermilion from Pewter. There are no points of interest along the cave; however, the cave is the only location where wild Diglett and the rare Dugtrio are found in Kanto.
The usefulness of the cave as a connector route between Routes 2 and 11 has allowed Diglett's Cave to become one of the most important non-numbered routes in the Pokémon world. In fact, after the player enters Cerulean City, the only way to return to Pewter City and Viridian City without using Surf or Fly is to travel through Diglett's Cave.
In Pokémon HeartGold and SoulSilver, Brock will come to the northern entrance and give passers-by his Pokégear phone number. Once defeated in a rematch he appears on late Saturday afternoon to offer a trade to the player.
In Generation III the cave was much longer than in any other generation.
In Generation IV the cave is the same length as it was in Generation II. This makes it one of very few Kanto areas to retain its length from Generation II. The only change is the addition of Rock Climb walls, that allow access to a higher level of the cave.
Diglett's Cave appeared in Great Success in the Mountains or the Seas!?. Red, Clefairy, and Pikachu enter the cave after Red and Clefairy's fighting over a rice ball causes the food to fly into the cave. After some exploring, Clefairy encounters a Diglett by stepping on its head. This results in a massive whack-a-mole scenario between the Diglett, Clefairy, and Pikachu, and causing the cave to collapse. However, Red's team manages to exit before heading to Vermilion City.
Interestingly enough, Red and his team encounter Diglett's Cave before Vermilion City, despite the fact that the cave must normally first be accessed by going through the city.
In Generation II only, the encounter rate of wild Pokémon in Diglett's Cave varies with the time of day: in the morning, it is twice as high as during daytime, and at nighttime, it is four times as high. It is the only location with varying encounter rates.