After you go west through Route 8 and go through the Underground Path, you reach Route 7.

Explore the Route

In the grass in this area, you can encounter Pidgey, Pidgeotto, Raticate, Jigglypuff, Vulpix, Abra, Porygon, and others.

To the right of the Underground Path exit, if one of your pokémon is following you, it will find a Nanab Berry in the bush.

East of there, you can battle Ace Trainer Yvette, who has a level 28 Raichu, a level 29 Dugtrio, and a level 28 Seel. You get 2800 Pokédollars and 5 Ultra Balls for winning.

To the right of the Ace Trainer, there is an Elixir.

There is a gatehouse to the east, but the guard won't let you through.

To the northwest, you can battle Coach Trainer Alpesh, who has a level 29 Farfetch'd and a level 30 Wigglytuff. You get 3000 Pokédollars for winning. After the battle, you get TM12 Facade.

Go west to reach Celadon City.