Go to the Pokemart, and you will be asked to deliver a package to Oak. After this, the old man will leave and you can pass through to Viridian Forest.
go through viridian forest
(Pewter city) through Viridian Forest
Viridian City.
Viridian city.
Viridian city.
Viridian city.
Viridian City.
Viridian City gym!!
Viridian City.
Beat the eighth Gym, which is in Viridian City!
On the upper left of Viridian City.
viridian city