Chapter 182 - 182: Diglett Cave
In reality, there are two paths from Saffron City to Vermilion City.
One is Route 6, the option most people are familiar with. Though it passes through a forest with many wild Pokémon, it also has a road specifically built by the Pokémon League, and its safety is routinely maintained.
Buses traveling from Vermilion City to Saffron City usually take this path, as it's quick and safe.
The other option is a more natural path, or rather, a tunnel.
Between Vermilion City and Saffron City, there is a large number of Diglett and Dugtrio. These Pokémon are peaceful by nature and love to be near humans.
They often dig in the ground, bringing various mineral elements to the surface that benefit plant and animal growth.
For this reason, both trainers and the community highly appreciate Diglett and Dugtrio, to the point that even Pokémon hunters and trainers from the dark world avoid harming them.
Disturbing a group of Diglett or Dugtrio could cause landslides or, in the worst case, alter the area's topography.
Thanks to these adorable, mostly non-aggressive Pokémon, a tunnel has been dug between Vermilion City and Saffron City.